The cover email for the patch series is getting a little unwieldy so I will provide a terser summary here, and just update the list of changes from version to version. Please see the previous versions linked by the In-Reply-To for more detailed comments about changes in earlier versions of the patch series.
v7: The main change in this version is a change in where we call task_isolation_enter(). The arm64 code only invokes the context_tracking code right at kernel entry, and right at kernel exit, and the exit point is too late for task isolation; one of my test cases, when run on arm64, showed that a signal delivered while task isolation is waiting for the timer interrupt to quiesce was not properly handled before returning to userspace. The tilegx code properly handled that case because it ran user_exit() in the work-pending loop. But since arm64 calls user_exit() later, it was too late to go back and handle the signal. I decided to make the task isolation work explicit in the "work" loop done on return to userspace, and although I could have done this by hacking up the arm64 assembly code for this purpose, I decided to follow the x86 approach and use the prepare_exit_to_usermode() model where architectures handles work looping in C code. I added that support to arm64 and tile as a pre-requisite change, then modified the loop in C to call task isolation appropriately. This both makes the slowpath return-to-user code more maintainable for arm64 and tile going forward, and also avoids some of the subtlety where the context tracking code was being asked to invoke task isolation at user_enter() time. As a result of this change, I have moved all the architecture-specific changes to individual patches: two patches to switch arm64 and tile to the prepare_exit_to_usermode() loop, and three patches (one each for x86, arm64, and tile) to add the necessary call to task_isolation(), plus changes to check at syscall entry for strict mode. In addition, since arm64 doesn't use exception_enter(), I added an explicit call to task_isolation_exception() in do_mem_abort() so that page faults would be properly flagged in strict mode. I also added an RCU_LOCKDEP_WARN() at Andy Lutomirski's suggestion. And, the patch series is rebased to v4.3-rc1. v6: restructured to be a "task_isolation" mode not a "cpu_isolated" mode (Frederic) v5: rebased on kernel v4.2-rc3 converted to use CONFIG_CPU_ISOLATED and separate .c and .h files incorporates Christoph Lameter's quiet_vmstat() call v4: rebased on kernel v4.2-rc1 added support for detecting CPU_ISOLATED_STRICT syscalls on arm64 v3: remove dependency on cpu_idle subsystem (Thomas Gleixner) use READ_ONCE instead of ACCESS_ONCE in tick_nohz_cpu_isolated_enter use seconds for console messages instead of jiffies (Thomas Gleixner) updated commit description for patch 5/5 v2: rename "dataplane" to "cpu_isolated" drop ksoftirqd suppression changes (believed no longer needed) merge previous "QUIESCE" functionality into baseline functionality explicitly track syscalls and exceptions for "STRICT" functionality allow configuring a signal to be delivered for STRICT mode failures move debug tracking to irq_enter(), not irq_exit() General summary: The existing nohz_full mode does a nice job of suppressing extraneous kernel interrupts for cores that desire it. However, there is a need for a more deterministic mode that rigorously disallows kernel interrupts, even at a higher cost in user/kernel transition time: for example, high-speed networking applications running userspace drivers that will drop packets if they are ever interrupted. These changes attempt to provide an initial draft of such a framework; the changes do not add any overhead to the usual non-nohz_full mode, and only very small overhead to the typical nohz_full mode. The kernel must be built with CONFIG_TASK_ISOLATION to take advantage of this new mode. A prctl() option (PR_SET_TASK_ISOLATION) is added to control whether processes have requested this stricter semantics, and within that prctl() option we provide a number of different bits for more precise control. Additionally, we add a new command-line boot argument to facilitate debugging where unexpected interrupts are being delivered from. Code that is conceptually similar has been in use in Tilera's Multicore Development Environment since 2008, known as Zero-Overhead Linux, and has seen wide adoption by a range of customers. This patch series represents the first serious attempt to upstream that functionality. Although the current state of the kernel isn't quite ready to run with absolutely no kernel interrupts (for example, workqueues on task_isolation cores still remain to be dealt with), this patch series provides a way to make dynamic tradeoffs between avoiding kernel interrupts on the one hand, and making voluntary calls in and out of the kernel more expensive, for tasks that want it. The series (based currently on v4.3-rc1) is available at: git://git.kernel.org/pub/scm/linux/kernel/git/cmetcalf/linux-tile.git dataplane Note: I have not removed the commit to disable the 1Hz timer tick fallback that was nack'ed by PeterZ, pending a decision on that thread as to what to do (https://lkml.org/lkml/2015/5/8/555); also since if we remove the 1Hz tick, task_isolation threads will never re-enter userspace since a tick will always be pending. Chris Metcalf (10): task_isolation: add initial support task_isolation: support PR_TASK_ISOLATION_STRICT mode task_isolation: provide strict mode configurable signal task_isolation: add debug boot flag nohz: task_isolation: allow tick to be fully disabled arch/x86: enable task isolation functionality arch/arm64: adopt prepare_exit_to_usermode() model from x86 arch/arm64: enable task isolation functionality arch/tile: adopt prepare_exit_to_usermode() model from x86 arch/tile: enable task isolation functionality Christoph Lameter (1): vmstat: provide a function to quiet down the diff processing Documentation/kernel-parameters.txt | 7 ++ arch/arm64/include/asm/thread_info.h | 18 +++-- arch/arm64/kernel/entry.S | 6 +- arch/arm64/kernel/ptrace.c | 10 ++- arch/arm64/kernel/signal.c | 36 +++++++--- arch/arm64/mm/fault.c | 8 +++ arch/tile/include/asm/processor.h | 2 +- arch/tile/include/asm/thread_info.h | 8 ++- arch/tile/kernel/intvec_32.S | 46 ++++--------- arch/tile/kernel/intvec_64.S | 49 +++++--------- arch/tile/kernel/process.c | 92 ++++++++++++++----------- arch/tile/kernel/ptrace.c | 3 + arch/tile/mm/homecache.c | 5 +- arch/x86/entry/common.c | 45 ++++++++++--- include/linux/context_tracking.h | 11 ++- include/linux/isolation.h | 42 ++++++++++++ include/linux/sched.h | 3 + include/linux/vmstat.h | 2 + include/uapi/linux/prctl.h | 8 +++ init/Kconfig | 20 ++++++ kernel/Makefile | 1 + kernel/context_tracking.c | 9 ++- kernel/irq_work.c | 5 +- kernel/isolation.c | 127 +++++++++++++++++++++++++++++++++++ kernel/sched/core.c | 21 ++++++ kernel/signal.c | 5 ++ kernel/smp.c | 4 ++ kernel/softirq.c | 7 ++ kernel/sys.c | 8 +++ kernel/time/tick-sched.c | 3 +- mm/vmstat.c | 14 ++++ 31 files changed, 477 insertions(+), 148 deletions(-) create mode 100644 include/linux/isolation.h create mode 100644 kernel/isolation.c -- 2.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
