the bitrig smpns branch has been created by haesbaert. it is 24 commits behind master, and 35 commits ahead.
commit 737240c4e0b85c743aa690debe2ca02f2f83bf5a diff: https://github.com/bitrig/bitrig/commit/737240c author: Christiano Haesbaert <[email protected]> date: Mon Jan 12 15:54:27 2015 +0100 Add P_ITHREAD to the string formatting bits. M sys/sys/proc.h commit 7adfa31a6fa5d5d2197de5a2c2e01cd22087b2b1 diff: https://github.com/bitrig/bitrig/commit/7adfa31 author: Christiano Haesbaert <[email protected]> date: Mon Jan 12 15:52:53 2015 +0100 Make sure we don't try to grab a bmtx with set P_SINTR. If we sleep on the bmtx with P_SINTR set, a signal might make us runnable, that is ilegal, assert it. M sys/kern/kern_bmtx.c M sys/kern/kern_synch.c M sys/kern/sched_bsd.c commit 733400d3323de8d3e6d7c79a3b7076dddff2734a diff: https://github.com/bitrig/bitrig/commit/733400d author: Christiano Haesbaert <[email protected]> date: Wed Dec 10 02:14:52 2014 +0100 Give device names to ithreads p_comm and evcounters to softintr. Concatenate all device names in the ithread's process name, this is useful for debugging and/or profiling. Also put event counters on software interrupts, I can't recall how many times I wanted to know this. A ps auxkl might show the following now: root 6034 0.0 0.0 0 0 ?? DK 2:01AM 0:04.97 (softclock) 0 0 0 -18 0 intr root 24717 0.0 0.0 0 0 ?? DK 2:01AM 0:01.06 (softnet) 0 0 0 -18 0 intr root 25481 0.0 0.0 0 0 ?? DK 2:01AM 0:01.08 (ehci0,mpi0) 0 0 0 -18 0 intr root 23688 0.0 0.0 0 0 ?? DK 2:01AM 0:01.02 (em0) 0 0 0 -18 0 intr .... M sys/dev/ic/com.c M sys/dev/usb/usb.c M sys/kern/kern_clock.c M sys/kern/kern_ithread.c M sys/kern/kern_softintr.c M sys/net/netisr.c M sys/net/pipex.c M sys/sys/softintr.h commit 76e60e7c4ceac2755943c106330875f287497823 diff: https://github.com/bitrig/bitrig/commit/76e60e7 author: Christiano Haesbaert <[email protected]> date: Mon Dec 8 23:36:55 2014 +0100 Cleanup softintr, remove establish_mpsafe now that IPL_FLAGS is here. Also kill unused softintr.c from amd64. ok pwildt@ D sys/arch/amd64/amd64/softintr.c M sys/kern/kern_softintr.c M sys/sys/softintr.h commit 7c0c271c3a0bce896aecc49b051ca90efef33610 diff: https://github.com/bitrig/bitrig/commit/7c0c271 author: Patrick Wildt <[email protected]> date: Sat Aug 23 22:52:57 2014 +0200 Revert to nearly the old softintr_ API, but keep ithreads for it. ok haesbaert@ M sys/arch/amd64/include/intr.h M sys/conf/files M sys/dev/ic/com.c M sys/dev/usb/usb.c M sys/kern/kern_clock.c M sys/kern/kern_ithread.c M sys/kern/kern_sig.c A sys/kern/kern_softintr.c M sys/net/netisr.c M sys/net/netisr.h M sys/net/pipex.c M sys/sys/ithread.h A sys/sys/softintr.h commit bda31336e4a0581630206d0eb640c49aa54d4b8f diff: https://github.com/bitrig/bitrig/commit/bda3133 author: M Farkas-Dyck <[email protected]> date: Mon Dec 8 09:47:29 2014 -0500 unbreak bmtx_fetch_and M sys/kern/kern_bmtx.c commit 10c8ebe86d6e6b44cdad860f731caf91457de189 diff: https://github.com/bitrig/bitrig/commit/10c8ebe author: Christiano Haesbaert <[email protected]> date: Fri Dec 5 12:38:03 2014 +0100 Hook kernel preemption back and allow "total" preemption. kernel.preemption = 2, will make any higher priority thread preempt the current thread, if and only if they are on the same cpu. Highly experimental, performance drops (since contention on kernel lock causes even more context switches). kernel.preemption = 1 still allows preemption just for interrupt threads. M sys/kern/kern_sysctl.c M sys/kern/sched_bsd.c commit 4a7d1bc7e5ae0530f835d53ba73235df2b3dce2c diff: https://github.com/bitrig/bitrig/commit/4a7d1bc author: Christiano Haesbaert <[email protected]> date: Thu Dec 4 18:56:17 2014 +0100 Use acq_rel in atomic_fetch_{or,and} for kern_bmtx. Also make wrapper around the atomic_c11 calls, code reads better. M sys/kern/kern_bmtx.c commit c2ac02a24734a4883e8930c12211f0049af66f40 diff: https://github.com/bitrig/bitrig/commit/c2ac02a author: Christiano Haesbaert <[email protected]> date: Thu Dec 4 17:03:58 2014 +0100 Use uintptr_t instead of u_long in kern_bmtx.c. M sys/kern/kern_bmtx.c commit 070b29c70e8d054382a9b2a334ab9f4ab7fdd578 diff: https://github.com/bitrig/bitrig/commit/070b29c author: Christiano Haesbaert <[email protected]> date: Tue Dec 2 19:21:36 2014 +0100 Simplify ithread_sleep() and ithread_run(). setrunnable() is less efficient since it does unecessary computations for a kthread. Even so, lets use it as it diminishes the amount of replicated code. M sys/kern/kern_ithread.c M sys/kern/sched_bsd.c M sys/sys/proc.h commit 50e0a6d010a29f82ea123984a814b3f013b41988 diff: https://github.com/bitrig/bitrig/commit/50e0a6d author: Christiano Haesbaert <[email protected]> date: Thu Oct 30 21:04:14 2014 +0100 crit_rundeferred() -> crit_unpend(), call MD intr_unpend(). Make crit_unpend() the function to be called everytime we leave a critical section, make it call intr_unpend() which is MD. Trying to keep the code in intr_unpend() MI now is unrealistic. M sys/arch/amd64/amd64/intr.c M sys/arch/amd64/amd64/spl.S M sys/arch/amd64/include/intr.h M sys/kern/kern_crit.c M sys/sys/proc.h commit 4ce8feacb8be75c3aeb9d58ba728f8c1d1ce3854 diff: https://github.com/bitrig/bitrig/commit/4ce8fea author: Christiano Haesbaert <[email protected]> date: Mon Sep 29 22:46:05 2014 +0200 Slightly more efficient crit_rundeferred(). Instead of disabling/enabling interrupts for every ipending intrsource, do it once and clear it. Another option is using atomic_exchange_explicit() but the bus locking is unecessary since this is a cpu local word. M sys/kern/kern_crit.c commit 7366c07aa492a0b01316e11fbab0cc9e9609aaca diff: https://github.com/bitrig/bitrig/commit/7366c07 author: Christiano Haesbaert <[email protected]> date: Sun Sep 28 12:23:23 2014 +0200 Be a bit more strict with KERNEL_LOCK ordering DIAGNOSTIC. Also make the loss of atomicity in pool_get() drop and reaquire the critical sections. This makes the kernel lock crit depth messages go away on boot. M sys/kern/kern_malloc.c M sys/kern/subr_pool.c M sys/sys/systm.h commit 854b82c8c6970e226b1f1e69da00a54ba6a59d8c diff: https://github.com/bitrig/bitrig/commit/854b82c author: Christiano Haesbaert <[email protected]> date: Sat Sep 27 13:01:27 2014 +0200 Kill CRITCOUNTERS left overs M sys/kern/kern_crit.c commit 50087d5be60efbad1fea6768b40ad0a5078e1408 diff: https://github.com/bitrig/bitrig/commit/50087d5 author: Christiano Haesbaert <[email protected]> date: Sat Sep 27 12:52:48 2014 +0200 Use the intr_ as prefix for interrupt API, intr_[disable|enable|...] Discussed with Patrick, we both agree this makes more sense than using a suffix. Also use intr_get_state() and intr_set_state() instead of state() and restore(). M sys/arch/amd64/amd64/amd64_mem.c M sys/arch/amd64/amd64/hibernate_machdep.c M sys/arch/amd64/amd64/i8259.c M sys/arch/amd64/amd64/ioapic.c M sys/arch/amd64/amd64/ipifuncs.c M sys/arch/amd64/amd64/lapic.c M sys/arch/amd64/amd64/lock_machdep.c M sys/arch/amd64/amd64/machdep.c M sys/arch/amd64/include/cpufunc.h M sys/arch/amd64/isa/clock.c M sys/dev/acpi/acpi.c M sys/dev/isa/gus.c M sys/kern/kern_crit.c M sys/kern/kern_sched.c commit 045e412d4b7b2d2893cc910cf83c258e861cfcaa diff: https://github.com/bitrig/bitrig/commit/045e412 author: Christiano Haesbaert <[email protected]> date: Tue Sep 16 20:21:46 2014 +0200 Add ithread.h and bmtx.h to distrib sets M distrib/sets/lists/base/md.amd64 M distrib/sets/lists/comp/mi commit 64f09a926cdd9b634c90a653602d09e6b557943c diff: https://github.com/bitrig/bitrig/commit/64f09a9 author: Christiano Haesbaert <[email protected]> date: Fri Aug 29 13:38:18 2014 +0200 Use more sensical labels on vector.S M sys/arch/amd64/amd64/vector.S commit 6826d2a71bced1d8ac32b4a03fab67abd88411fa diff: https://github.com/bitrig/bitrig/commit/6826d2a author: Christiano Haesbaert <[email protected]> date: Wed Aug 27 20:18:12 2014 +0200 Give names to bmtx locks and introduce a bmtx_dump(). The name of the lock is saved on p_wmesg in case the process is waiting for the lock. M sys/kern/kern_bmtx.c M sys/kern/kern_lock.c M sys/sys/bmtx.h commit 3fa361a4b1e35f5adb389f3e37dae4d3fe2761d3 diff: https://github.com/bitrig/bitrig/commit/3fa361a author: Christiano Haesbaert <[email protected]> date: Wed Aug 27 18:21:02 2014 +0200 Decouple the idea of masking/unmasking an intrsource from pic{}. When we take an interrupt, we mask the source and schedule the thread, when the thread eventually runs and finishes processing, it unmasks the source. So there must be a way of unmasking the source in a MI fashion, each architecture should have a intrsource_unmask() function. In amd64, we just map it to the corresponding pic{} callback. M sys/arch/amd64/include/intr.h M sys/kern/kern_ithread.c commit 60ed6cdfb5a0e2436a71abcb2eacb189491d7a92 diff: https://github.com/bitrig/bitrig/commit/60ed6cd author: Christiano Haesbaert <[email protected]> date: Wed Aug 27 18:06:11 2014 +0200 Fix interrupt account with intr_shared_edge != 0. M sys/kern/kern_ithread.c commit 12c6932f3eacf09062a74878993439a5be48b9c4 diff: https://github.com/bitrig/bitrig/commit/12c6932 author: Christiano Haesbaert <[email protected]> date: Wed Aug 27 15:49:12 2014 +0200 Whitespace & wording M sys/kern/kern_ithread.c commit e41ef3f15826a949e6694fc02bb332d5da9522be diff: https://github.com/bitrig/bitrig/commit/e41ef3f author: Christiano Haesbaert <[email protected]> date: Wed Aug 27 14:50:15 2014 +0200 Introduce intr_state_t and MI "API" for blocking interrupts. The fact that disabling/enabling real interrupts is totally MD makes writing portable code harder, here I propose the following API: enable_intr(void) Enables "all" hw interrupts. disable_intr(void) Disables "all" hw interrupts. intr_state_t state_intr(void) Reads hw interrupts state. restore_intr(intr_state_t) Restore hw interrupts state. I think this should map easily to arm or any other future platform, intr_state_t should be defined to whatever is convenient to the arch. Switch crit_rundeferred() to use it, when we port stuff to arm, we just need to mimick the API. M sys/arch/amd64/include/cpufunc.h M sys/kern/kern_crit.c commit 017619ace9f44e11aedc8f1036cc6412b88cfcb0 diff: https://github.com/bitrig/bitrig/commit/017619ac author: Christiano Haesbaert <[email protected]> date: Tue Aug 26 16:13:16 2014 +0200 Kill is_minlevel & is_maxlevel from intrsource{}. This is a step into turning intrsource{} MI and getting rid of the IPL leftovers. M sys/arch/amd64/amd64/acpi_machdep.c M sys/arch/amd64/amd64/genassym.cf M sys/arch/amd64/amd64/intr.c M sys/arch/amd64/amd64/machdep.c M sys/arch/amd64/include/intr.h M sys/arch/amd64/include/segments.h M sys/kern/kern_ithread.c commit 3f9457edfcb32d295b3ab22c0e58f0084343780b diff: https://github.com/bitrig/bitrig/commit/3f9457e author: Christiano Haesbaert <[email protected]> date: Fri Jun 27 16:27:14 2014 +0200 Turnstile lock implementation, turn kernel lock into one. BMTX stands for "blocking mutex", and it's implemented as a turnstile exclusive recursive lock. The Kernel Lock has been made a bmtx. Background ~~~~~~~~~~ I've been tracking the performance impacts of the smpns changes and the one thing who really hurt performance was turning kernel lock into a rrwlock. The number of IPIs when building the kernel or world would go over 5k/s, much higher than the <1k/s of the original mplock implementation. That should be no surprise, since rrwlock is an always sleeping lock which goes through wakeup/tsleep on every contention. Performance also degraded considerably, baseline would build an image in ~4m, taking ~5m25s after the change to rrwlock. Therefore, the motivation for a turnstile lock was pure performance wise, as they hold the same semantics as a sleeping lock like rwlock. Semantics ~~~~~~~~~ o Bmtx uses no critical section and doesn't block interrupts on any way, they are resilient to preemption. They are adequate to interlock against interrupt threads, so that should become the normal lock throughout the kernel. This is the attempt of having synchronous locking across interrupts and kernel threads. o Recursion is allowed, options for forbiding it in the future should be discussed. o Interleaving on unlocking is allowed, the following is legal: bmtx_lock(a); bmtx_lock(b); bmtx_unlock(a); OR bmtx_unlock(b); bmtx_unlock(b); bmtx_unlock(a); o Sleeping with a bmtx held is legal. Implementation ~~~~~~~~~~~~~~ o The cost for an uncontested operation is never higher than the maximum cost of a single compare-and-set operation, average cost on a cached situation is less than 50cycles per pair of lock/unlock on my haswell i5 2.4ghz, considering function call overhead to be 0. We can easily cut the function call overhead by making the function into a macro that just tries the fast operation outside (one compare-and-set call), if it fails, it calls into the function. o Bmtx synchronizes across one atomic word called bmtx_lock, in which we store: >From bits 2-31 or 2-63: the curproc address structure. The first two bits are abused to store two flags which are not mutually exclusive. BMTX_RECURSE - signals that this bmtx was recursed. BMTX_WAITERS - signals that there are sleepers waiting for the acquisition of the lock. o Bmtx is a turnstile lock since it tries to spin _as long_ as the owner of the lock is currently _running_ on another cpu. Under all other conditions, the caller blocks. Blocking means setting the BMTX_WAITERS in the atomic word and inserting itself in the bmtx's waitqueue. o To be able to block on the lock, we can't depend only on the atomic word, we need a way to interlock with the other cpu, so that we don't miss a wakeup. This is implemented using SCHED_LOCK as an interlock, this allows us to overcome the lost-wakeup race. The algorithm is something like this: 1 spin on the lock until holder is not SONPROC (running). The test for SONPROC is done on a racy fashion, which follows the process structure and checks p->p_stat. 2 If we think the owner appears to not be SONPROC, we interlock with the SCHED_LOCK and _retest_ the condition, therefore, recovering from the race. 3 Assuming the owner is indeed blocked, we set BMTX_WAITERS and put ourselves in the queue. On the unlock path, the fast path only attempts to clear ownership if BMTX_WAITERS is _not_ set, if it is, we need the slower path, where we interlock with SCHED_LOCK, saving ourselves from the race. In the future, when the scheduler doesn't suck horse-ass, we will interlock with an arbitrary lock, something like a stripelock, instead of a global SCHED_LOCK. We could do it with mutexes and msleep now, but this is so ridiculous as it's just another lock to pass ownership for the SCHED_LOCK. A performant implementation requires the scheduler to expose the underlying interlock to the caller. CAVEATS ~~~~~~~ On the lock path, when testing if the owner is SONPROC, we have the following comment: /* XXX if we are preempted here, high chance p might have gone and * we're fucked. This is an "accepted" race in freebsd because of the * way they recycle the td structures, it might not be to us. We could * think of a crit_enter()/crit_leave(). We can not safely test p and deference p->p_stat, the process might have gone through sched_exit() and p might be freed, the timing would have to be very very very evil, I've never hit this situation and I'm buying it for now. Alternative solutions is changing the way we alocate proc{} (like freebsd), or keeping track of all held mutexes and updating a state on the mutex itself saying "OWNER_IS_RUNNING". Results ~~~~~~~ My building times went to be as performant as baseline, sometimes slightly faster, I could only test this in vmware so far, so I can't have precise numbers. I would go as far as saying that it is _no_ worse than the baseline kernel. Building time improved around 25% against the rrwlock implementation. IPIs were reduced from 5000-6000 to 200-1200/s. Statistics ~~~~~~~~~~ I've collected the number of fast vs slow paths by defining BMTX_STATS on the lock, as shown below, the number of slow paths are insignificant compared to the fast paths: bmtx_fast_locks 21017802 bmtx_fast_unlocks 31133706 bmtx_recursed_locks 524294 bmtx_recursed_unlocks 524279 bmtx_lock_blocks 33174 bmtx_lock_blocks_cancelled 29742 bmtx_lock_blocks_slept 3862 bmtx_spun_locks 10117383 bmtx_blocked_unlocks 3866 bmtx_unlock_has_waiter 3866 M sys/conf/files A sys/kern/kern_bmtx.c M sys/kern/kern_lock.c A sys/sys/bmtx.h M sys/sys/mplock.h M sys/sys/systm.h commit ff8d58175d4427ea881c7a9bbb71ce8c82b1b929 diff: https://github.com/bitrig/bitrig/commit/ff8d581 author: Christiano Haesbaert <[email protected]> date: Fri Jun 6 11:42:01 2014 +0200 Stop using the sleepqueue for interrupt threads. There is no need for it, it cuts some hacks and it's less instructions. Since we always wakeup from ithread_run(), we always know the proc to awake, the solely point of the sleepqueue is to be a storage to be found via ident hashing. M sys/kern/kern_ithread.c commit ad9758b0e3ca8c8db505c09b38bb6310a9f29081 diff: https://github.com/bitrig/bitrig/commit/ad9758b author: Christiano Haesbaert <[email protected]> date: Sun May 11 17:22:11 2014 +0200 No need for running interrupt handlers in critical sections anymore. Preemption correctly relies on the priority to do preemption, having a ithread->ithread preemption due to ithread sleeping at a lower priority should be ok. M sys/kern/kern_ithread.c commit ecb419df73f041fe5db7eaa1df8956b10fae8d22 diff: https://github.com/bitrig/bitrig/commit/ecb419d author: Christiano Haesbaert <[email protected]> date: Sat Mar 1 11:08:55 2014 +0100 Initial kernel preemption. This diff introduces a rudimentary form of kernel preemption, it allows interrupt threads to preempt other kernel processing, like userland doing syscalls or other normal kthreads. Preemption is deferred if the current process is in a critical section. When curproc preempts: o It must not be stolen to run on another cpu, it is still SRUNable, but must therefore be pinned to the curcpu() runqueue. o It must continue to hold all the locks it had, in our case: rwlocks, including kernel lock. o In case the _preempting_ process (not the preempted) tries to acquire the kernel lock, but the holder was preempted, the _preempting_ process blocks so that the _preempted_ might be resumed. CAVEATS: o The way we test for preemption is still primitive, I'll only be able to attack this properly once I introduce proper APIs into the scheduler, but for that I want to make the scheduler modular, so that we are able to play with different schedulers. So we need MORE APIs, not LESS as _some_ people believe. o ci_want_resched which is responsible for preempting userland is still present as at this point we need it, once I'm able to hack the scheduler there should be only one way of preemption, so it will look a bit funky until there. Also introduce a sysctl (kern.preemption) which enables us to activate or deactivate kernel preemption. M sys/kern/kern_crit.c M sys/kern/kern_exit.c M sys/kern/kern_ithread.c M sys/kern/kern_ktrace.c M sys/kern/kern_sched.c M sys/kern/kern_subr.c M sys/kern/kern_sysctl.c M sys/kern/sched_bsd.c M sys/kern/subr_xxx.c M sys/sys/proc.h M sys/sys/sched.h M sys/sys/syscall_mi.h M sys/sys/sysctl.h M sys/uvm/uvm_glue.c commit 83794fffe5200ac580573304aec5d1251ad507d0 diff: https://github.com/bitrig/bitrig/commit/83794ff author: Christiano Haesbaert <[email protected]> date: Wed Feb 26 23:24:37 2014 +0100 Newly formed processes should start in a critical section. They have the schedlock, and release on proc_trampoline_mp(), if the newly formed process is not in a critical section, a clock interrupt might attempt to grab the SCHED LOCK, or worse, we might preempt to early in the future. This paves the way for preemption and allows SCHED LOCK to be a mutex, we only need guenther's fix for the recursive tsleep. M sys/kern/kern_fork.c M sys/sys/proc.h commit 315f93f1ef34b8408ef4d9e43bdcf1d9db5b0708 diff: https://github.com/bitrig/bitrig/commit/315f93f author: Christiano F. Haesbaert <[email protected]> date: Sat Feb 1 16:20:50 2014 +0100 Convert kernel lock to a rrwlock. Introduce rrw_exit_all(), rrw_enter_cnt() and rw_held()/rrw_held(). Also, make the assert unlocked functions make sense, now we assert that _we_ don't hold the lock, asserting that no one has the lock is impossible. We can't sleep on proc_trampoline_mp for the idle process, since it should never be in a sleepqueue, I had to introduce a hack to make it not acquire the kernel lock. The correct fix is to pass a flag to fork1() that gets propagated to proc_trampoline_mp(). M sys/arch/amd64/amd64/intr.c M sys/arch/amd64/amd64/ipifuncs.c M sys/kern/kern_fork.c M sys/kern/kern_ithread.c M sys/kern/kern_lock.c M sys/kern/kern_rwlock.c M sys/kern/kern_sched.c M sys/kern/kern_synch.c M sys/sys/mplock.h M sys/sys/rwlock.h M sys/sys/systm.h commit d481655030a3de61def0a0f24fda084287d24d45 diff: https://github.com/bitrig/bitrig/commit/d481655 author: Christiano F. Haesbaert <[email protected]> date: Tue Dec 31 02:23:56 2013 +0100 Fix compilation of !MULTIPROCESSOR. Armani had fixed this a while ago in the old Openbsd tree, this is just an updated version of his diff. spotted by aalm. M sys/kern/sched_bsd.c M sys/sys/systm.h commit cbfcb95474b803d79daaed75110f288b980ca942 diff: https://github.com/bitrig/bitrig/commit/cbfcb95 author: Christiano F. Haesbaert <[email protected]> date: Mon Dec 30 01:32:35 2013 +0100 Remove __mp_release_all_but_one(). M sys/arch/amd64/amd64/lock_machdep.c M sys/arch/amd64/include/mplock.h M sys/sys/mplock.h commit 7daabe6352c9ba6bb6cdba475fd165151cbe5c98 diff: https://github.com/bitrig/bitrig/commit/7daabe6 author: Christiano F. Haesbaert <[email protected]> date: Mon Dec 30 01:27:11 2013 +0100 Make so that mi_switch() won't relock sched_lock. The caller needs to reacquire it if desired. More complex paths like proc_stop() were left like before, so they reacquire the lock. Almost every user of mi_switch() just do a SCHED_UNLOCK() after return, so this commit prevents a LOCK/UNLOCK on a contented lock. For this to work, you can never mi_switch with a recursive sched_lock, and this is asserted. Thanks to grunk@ for questioning me on the diff and finding a bug which should fix suspend/resume, it was a double acquisition of SCHED_LOCK on sched_idle(). natano@ reported the bug. M sys/kern/kern_ithread.c M sys/kern/kern_sched.c M sys/kern/kern_sig.c M sys/kern/kern_synch.c M sys/kern/sched_bsd.c commit 16d99debc1f7379fedafcc3efcc55974f7ee4440 diff: https://github.com/bitrig/bitrig/commit/16d99de author: Christiano F. Haesbaert <[email protected]> date: Mon Dec 30 01:21:49 2013 +0100 Make __mp_lock_held() return the lock depth. M sys/arch/amd64/amd64/lock_machdep.c commit ae6b02d53b05c0b0686138e8a975bcbc1d18ee82 diff: https://github.com/bitrig/bitrig/commit/ae6b02d author: Christiano F. Haesbaert <[email protected]> date: Mon Dec 30 00:39:49 2013 +0100 Rework the SCHED_LOCK vs KERNEL_LOCK dance in mi_switch(). This avoids the lock/relock to fix lock ordering on mi_switch for all the cases except one. Before the idea was: - mi_switch() releases all kernel locks before context switching. - save the count in the stack. - context switch with SCHED_LOCK held. - wakeup, but to assure lock ordering it needs to: - release SCHED_LOCK - reacquire KERNEL_LOCK - acquire SCHED_LOCK With this diff, the caller is responsible for doing this, so you can't enter mi_switch with kernel lock now, you must release/reacquire yourself, being careful to always grab SCHED_LOCK before releasing the kernel locks, if not you lose atomicity before you can. Since we can grab kernel lock within a critical section, KERNEL_RELOCK_ALL must do the release/reenter dance. Next step is to make mi_switch() return with SCHED_LOCK unlocked, if the caller wants it is his job, he _already_ lost atomicity. Most of the cases mi_switch() relocks SCHED_LOCK only for the caller to unlock it, which is pretty stupid. M sys/kern/kern_ithread.c M sys/kern/kern_lock.c M sys/kern/kern_sched.c M sys/kern/kern_sig.c M sys/kern/kern_synch.c M sys/kern/sched_bsd.c M sys/sys/proc.h M sys/sys/systm.h commit 16c1b67b539f34f069f66e53058897759c18c32d diff: https://github.com/bitrig/bitrig/commit/16c1b67 author: Christiano F. Haesbaert <[email protected]> date: Sat May 25 13:19:17 2013 +0200 New interrupt model, move away from IPLs. This diff changes the interrupt model to something very similar to what other modern unixes like Solaris, FreeBSD, DragonflyBSD and linux. It also introduces critical sections. Interrupts except clock and ipi are handled by interrupt threads, when an interrupt fires, the only job for the small interrupt stub is to schedule the corresponding interrupt thread, when the ithread gets scheduled, it services the interrupt. The kernel must be made preemptive, so that interrupt threads may preempt the current running code. In this model, you normally never block interrupts, you rely solely on locks to protect the code, if the ithread preempts the running code, and it tries to acquire a contested lock, it blocks (sleeps) and gets resumed only when that lock is released. This allows us to have lower interrupt latency, as instead of blocking interrupts for a long section, you can fine grain that section in a specific lock. Instead of raising to IPL_BIO and preventing softclock from running for example, we can make softclock preempt the old IPL_BIO and only block if there is an actual lock contention. This was first implemented in Solaris 2 (Kleiman & Eykholt circa 93), they demonstrated that this model, after properly locked, changed the worst case latency from 1s to <1ms on a single-core 40mhz machine. It also allows for us to properly fight livelocks in the future, as the scheduler will make sure "everything runs at some point". The the kernel can now be synchronous with regard to locking, as you can use the same lock to interlock against interrupts or other normal kthreads. You can only block on locks if you have a process context, so you still need a way to block interrupts from normal (read: not ithread interrupts), like clock and ipi. For that we introduce critical sections, which block everything, in practice they're only used to protect scheduler data and on mutexes, so they are very short. In the future critical sections will also be the only thing that prevents kernel preemption. In order to prevent deadlocks, you must never be preempted while holding a spinlock, so a critical section is implied there, this is also akin to what every system does. In this present state, kernel preemption has not been implemented, all threads <IPL_CLOCK were moved to ithreads, there is no observable loss of performance, it's been stable since the last half a year. All spl calls <IPL_CLOCK were made no-ops, while >= IPL_CLOCK were replaced by critical sections. Most of the old assembly code has been rewritten in C, just because I refuse to maintain unecessary asm blocks. The next steps are: o Turn kernel lock into a rrwlock. o Enable kernel preemption, at this point all the interrupt interlocking will be done through kernel lock. o Decide on which subsystem to release first, having a wide subsytem lock. Make sure we have a process context early and kill crit_escaped. This was lost in a merge. M sys/arch/amd64/amd64/cpu.c M sys/arch/amd64/amd64/db_interface.c M sys/arch/amd64/amd64/fpu.c M sys/arch/amd64/amd64/genassym.cf M sys/arch/amd64/amd64/intr.c M sys/arch/amd64/amd64/ipi.c M sys/arch/amd64/amd64/lapic.c M sys/arch/amd64/amd64/locore.S M sys/arch/amd64/amd64/machdep.c M sys/arch/amd64/amd64/spl.S M sys/arch/amd64/amd64/trap.c M sys/arch/amd64/amd64/vector.S M sys/arch/amd64/amd64/via.c M sys/arch/amd64/conf/files.amd64 M sys/arch/amd64/include/atomic.h M sys/arch/amd64/include/cpu.h M sys/arch/amd64/include/frame.h M sys/arch/amd64/include/frameasm.h M sys/arch/amd64/include/intr.h M sys/arch/amd64/include/intrdefs.h M sys/arch/amd64/isa/clock.c M sys/arch/arm/arm/db_interface.c M sys/arch/arm/arm/pmap.c M sys/conf/files M sys/dev/acpi/acpi.c M sys/dev/cardbus/cardbus.c M sys/dev/ic/com.c M sys/dev/ic/comvar.h M sys/dev/ic/elink3.c M sys/dev/ic/i82365.c M sys/dev/ic/vga.c M sys/dev/ic/vga_subr.c M sys/dev/isa/if_ef_isapnp.c M sys/dev/isa/pcppi.c M sys/dev/onewire/onewire_bitbang.c M sys/dev/pci/drm/drm_atomic.h M sys/dev/pci/drm/radeon/radeon_kms.c M sys/dev/pci/mbg.c M sys/dev/pci/pccbb.c M sys/dev/pci/pci.c M sys/dev/pci/pci_map.c M sys/dev/pci/pciide.c M sys/dev/pcmcia/if_xe.c M sys/dev/rasops/rasops.c M sys/dev/sdmmc/sdmmc_io.c M sys/dev/usb/ehci.c M sys/dev/usb/ohci.c M sys/dev/usb/uhci.c M sys/dev/usb/umidi.c M sys/dev/usb/usb.c M sys/dev/usb/usbdivar.h M sys/dev/usb/usbf_subr.c M sys/dev/usb/usbfvar.h M sys/dev/usb/xhci.c M sys/dev/wsfont/wsfont.c M sys/kern/init_main.c M sys/kern/kern_clock.c A sys/kern/kern_crit.c M sys/kern/kern_event.c M sys/kern/kern_exec.c M sys/kern/kern_fork.c A sys/kern/kern_ithread.c M sys/kern/kern_lock.c M sys/kern/kern_mutex.c M sys/kern/kern_proc.c M sys/kern/kern_resource.c M sys/kern/kern_sched.c M sys/kern/kern_sensors.c M sys/kern/kern_sig.c M sys/kern/kern_synch.c M sys/kern/kern_time.c M sys/kern/kern_timeout.c M sys/kern/sched_bsd.c M sys/kern/subr_disk.c M sys/kern/subr_evcount.c M sys/kern/subr_hibernate.c M sys/kern/subr_log.c M sys/kern/subr_pool.c M sys/kern/subr_prf.c M sys/kern/subr_prof.c M sys/kern/subr_xxx.c M sys/kern/sys_generic.c M sys/kern/sys_process.c M sys/kern/vfs_subr.c M sys/kern/vfs_sync.c M sys/lib/libkern/libkern.h M sys/net/if_tun.c M sys/net/netisr.c M sys/net/netisr.h M sys/net/pipex.c A sys/sys/ithread.h M sys/sys/proc.h M sys/sys/sched.h M sys/sys/systm.h M sys/sys/timeout.h M sys/uvm/uvm_map.c
