On 02/12/20(Wed) 17:27, Jonathan Matthew wrote:
> On Tue, Dec 01, 2020 at 02:35:18PM -0300, Martin Pieuchot wrote:
> > On 01/12/20(Tue) 15:30, Claudio Jeker wrote:
> > > [...]
> > > Did you run a make build with that smr_barrier() in it and checked that it
> > > does not cause a slow down? I am sceptical, smr_barrier() is a very slow
> > > construct which introduces large delays and should be avoided whenever
> > > possible.
> >
> > I did build GENERIC.MP multiple times on a 4CPU sparc64 with the diff
> > below, without noticeable difference.
> >
> > I'm happy to hear from sceptical performance checkers :o)
>
> On a reasonably fast amd64 box, this increases GENERIC.MP make -j6 build time
> from
> ~3m06s to ~3m44s, which seems a bit much to me.
Do you know if this is due to an increase of %spin time?
> Replacing smr_barrier() with smr_flush() reduces the overhead to a couple of
> seconds, and it seems warranted here.
Could you try the diff below that only call smr_barrier() for multi-
threaded processes with threads still in the list. I guess this also
answers guenther@'s question. The same could be done with smr_flush().
diff --git lib/libkvm/kvm_proc2.c lib/libkvm/kvm_proc2.c
index 96f7dc91b92..1f4f9b914bb 100644
--- lib/libkvm/kvm_proc2.c
+++ lib/libkvm/kvm_proc2.c
@@ -341,8 +341,9 @@ kvm_proclist(kvm_t *kd, int op, int arg, struct process *pr,
kp.p_pctcpu = 0;
kp.p_stat = (process.ps_flags & PS_ZOMBIE) ? SDEAD :
SIDL;
- for (p = TAILQ_FIRST(&process.ps_threads); p != NULL;
- p = TAILQ_NEXT(&proc, p_thr_link)) {
+ for (p = SMR_TAILQ_FIRST_LOCKED(&process.ps_threads);
+ p != NULL;
+ p = SMR_TAILQ_NEXT_LOCKED(&proc, p_thr_link)) {
if (KREAD(kd, (u_long)p, &proc)) {
_kvm_err(kd, kd->program,
"can't read proc at %lx",
@@ -376,8 +377,8 @@ kvm_proclist(kvm_t *kd, int op, int arg, struct process *pr,
if (!dothreads)
continue;
- for (p = TAILQ_FIRST(&process.ps_threads); p != NULL;
- p = TAILQ_NEXT(&proc, p_thr_link)) {
+ for (p = SMR_TAILQ_FIRST_LOCKED(&process.ps_threads); p != NULL;
+ p = SMR_TAILQ_NEXT_LOCKED(&proc, p_thr_link)) {
if (KREAD(kd, (u_long)p, &proc)) {
_kvm_err(kd, kd->program,
"can't read proc at %lx",
diff --git sys/kern/exec_elf.c sys/kern/exec_elf.c
index 5e455208663..575273b306c 100644
--- sys/kern/exec_elf.c
+++ sys/kern/exec_elf.c
@@ -85,6 +85,7 @@
#include <sys/signalvar.h>
#include <sys/stat.h>
#include <sys/pledge.h>
+#include <sys/smr.h>
#include <sys/mman.h>
@@ -1360,7 +1361,7 @@ coredump_notes_elf(struct proc *p, void *iocookie, size_t
*sizep)
* threads in the process have been stopped and the list can't
* change.
*/
- TAILQ_FOREACH(q, &pr->ps_threads, p_thr_link) {
+ SMR_TAILQ_FOREACH_LOCKED(q, &pr->ps_threads, p_thr_link) {
if (q == p) /* we've taken care of this thread */
continue;
error = coredump_note_elf(q, iocookie, ¬esize);
diff --git sys/kern/init_main.c sys/kern/init_main.c
index fed6be19435..2b657ffe328 100644
--- sys/kern/init_main.c
+++ sys/kern/init_main.c
@@ -519,7 +519,7 @@ main(void *framep)
*/
LIST_FOREACH(pr, &allprocess, ps_list) {
nanouptime(&pr->ps_start);
- TAILQ_FOREACH(p, &pr->ps_threads, p_thr_link) {
+ SMR_TAILQ_FOREACH_LOCKED(p, &pr->ps_threads, p_thr_link) {
nanouptime(&p->p_cpu->ci_schedstate.spc_runtime);
timespecclear(&p->p_rtime);
}
diff --git sys/kern/kern_exit.c sys/kern/kern_exit.c
index a20775419e3..8cde5eca266 100644
--- sys/kern/kern_exit.c
+++ sys/kern/kern_exit.c
@@ -63,6 +63,7 @@
#ifdef SYSVSEM
#include <sys/sem.h>
#endif
+#include <sys/smr.h>
#include <sys/witness.h>
#include <sys/mount.h>
@@ -161,7 +162,9 @@ exit1(struct proc *p, int xexit, int xsig, int flags)
}
/* unlink ourselves from the active threads */
- TAILQ_REMOVE(&pr->ps_threads, p, p_thr_link);
+ SMR_TAILQ_REMOVE_LOCKED(&pr->ps_threads, p, p_thr_link);
+ if (!SMR_TAILQ_EMPTY_LOCKED(&pr->ps_threads))
+ smr_barrier();
if ((p->p_flag & P_THREAD) == 0) {
/* main thread gotta wait because it has the pid, et al */
while (pr->ps_refcnt > 1)
@@ -724,7 +727,7 @@ process_zap(struct process *pr)
if (pr->ps_ptstat != NULL)
free(pr->ps_ptstat, M_SUBPROC, sizeof(*pr->ps_ptstat));
pool_put(&rusage_pool, pr->ps_ru);
- KASSERT(TAILQ_EMPTY(&pr->ps_threads));
+ KASSERT(SMR_TAILQ_EMPTY_LOCKED(&pr->ps_threads));
lim_free(pr->ps_limit);
crfree(pr->ps_ucred);
pool_put(&process_pool, pr);
diff --git sys/kern/kern_fork.c sys/kern/kern_fork.c
index 9fb239bc8b4..e1cb587b2b8 100644
--- sys/kern/kern_fork.c
+++ sys/kern/kern_fork.c
@@ -52,6 +52,7 @@
#include <sys/acct.h>
#include <sys/ktrace.h>
#include <sys/sched.h>
+#include <sys/smr.h>
#include <sys/sysctl.h>
#include <sys/pool.h>
#include <sys/mman.h>
@@ -179,8 +180,8 @@ process_initialize(struct process *pr, struct proc *p)
{
/* initialize the thread links */
pr->ps_mainproc = p;
- TAILQ_INIT(&pr->ps_threads);
- TAILQ_INSERT_TAIL(&pr->ps_threads, p, p_thr_link);
+ SMR_TAILQ_INIT(&pr->ps_threads);
+ SMR_TAILQ_INSERT_TAIL_LOCKED(&pr->ps_threads, p, p_thr_link);
pr->ps_refcnt = 1;
p->p_p = pr;
@@ -557,7 +558,7 @@ thread_fork(struct proc *curp, void *stack, void *tcb,
pid_t *tidptr,
LIST_INSERT_HEAD(&allproc, p, p_list);
LIST_INSERT_HEAD(TIDHASH(p->p_tid), p, p_hash);
- TAILQ_INSERT_TAIL(&pr->ps_threads, p, p_thr_link);
+ SMR_TAILQ_INSERT_TAIL_LOCKED(&pr->ps_threads, p, p_thr_link);
/*
* if somebody else wants to take us to single threaded mode,
diff --git sys/kern/kern_proc.c sys/kern/kern_proc.c
index 70b781e53cb..a2acc741834 100644
--- sys/kern/kern_proc.c
+++ sys/kern/kern_proc.c
@@ -502,7 +502,7 @@ db_kill_cmd(db_expr_t addr, int have_addr, db_expr_t count,
char *modif)
return;
}
- p = TAILQ_FIRST(&pr->ps_threads);
+ p = SMR_TAILQ_FIRST_LOCKED(&pr->ps_threads);
/* Send uncatchable SIGABRT for coredump */
sigabort(p);
@@ -558,7 +558,7 @@ db_show_all_procs(db_expr_t addr, int haddr, db_expr_t
count, char *modif)
while (pr != NULL) {
ppr = pr->ps_pptr;
- TAILQ_FOREACH(p, &pr->ps_threads, p_thr_link) {
+ SMR_TAILQ_FOREACH_LOCKED(p, &pr->ps_threads, p_thr_link) {
#ifdef MULTIPROCESSOR
if (__mp_lock_held(&kernel_lock, p->p_cpu))
has_kernel_lock = 1;
diff --git sys/kern/kern_resource.c sys/kern/kern_resource.c
index 0111bfa733a..811b8434365 100644
--- sys/kern/kern_resource.c
+++ sys/kern/kern_resource.c
@@ -212,7 +212,7 @@ donice(struct proc *curp, struct process *chgpr, int n)
return (EACCES);
chgpr->ps_nice = n;
SCHED_LOCK(s);
- TAILQ_FOREACH(p, &chgpr->ps_threads, p_thr_link) {
+ SMR_TAILQ_FOREACH_LOCKED(p, &chgpr->ps_threads, p_thr_link) {
setpriority(p, p->p_estcpu, n);
}
SCHED_UNLOCK(s);
@@ -488,7 +488,7 @@ dogetrusage(struct proc *p, int who, struct rusage *rup)
memset(rup, 0, sizeof(*rup));
/* add on all living threads */
- TAILQ_FOREACH(q, &pr->ps_threads, p_thr_link) {
+ SMR_TAILQ_FOREACH_LOCKED(q, &pr->ps_threads, p_thr_link) {
ruadd(rup, &q->p_ru);
tuagg(pr, q);
}
diff --git sys/kern/kern_sig.c sys/kern/kern_sig.c
index 0cd78b46de5..c378aefd48f 100644
--- sys/kern/kern_sig.c
+++ sys/kern/kern_sig.c
@@ -925,7 +925,7 @@ ptsignal(struct proc *p, int signum, enum signal_type type)
* delayed. Otherwise, mark it pending on the
* main thread.
*/
- TAILQ_FOREACH(q, &pr->ps_threads, p_thr_link) {
+ SMR_TAILQ_FOREACH_LOCKED(q, &pr->ps_threads,
p_thr_link) {
/* ignore exiting threads */
if (q->p_flag & P_WEXIT)
continue;
@@ -1009,7 +1009,7 @@ ptsignal(struct proc *p, int signum, enum signal_type
type)
* XXX delay processing of SA_STOP signals unless action == SIG_DFL?
*/
if (prop & (SA_CONT | SA_STOP) && type != SPROPAGATED)
- TAILQ_FOREACH(q, &pr->ps_threads, p_thr_link)
+ SMR_TAILQ_FOREACH_LOCKED(q, &pr->ps_threads, p_thr_link)
if (q != p)
ptsignal(q, signum, SPROPAGATED);
@@ -2026,7 +2026,8 @@ single_thread_set(struct proc *p, enum single_thread_mode
mode, int deep)
pr->ps_singlecount = 0;
membar_producer();
pr->ps_single = p;
- TAILQ_FOREACH(q, &pr->ps_threads, p_thr_link) {
+ smr_read_enter();
+ SMR_TAILQ_FOREACH(q, &pr->ps_threads, p_thr_link) {
if (q == p)
continue;
if (q->p_flag & P_WEXIT) {
@@ -2072,6 +2073,7 @@ single_thread_set(struct proc *p, enum single_thread_mode
mode, int deep)
break;
}
}
+ smr_read_leave();
SCHED_UNLOCK(s);
if (mode != SINGLE_PTRACE)
@@ -2118,7 +2120,7 @@ single_thread_clear(struct proc *p, int flag)
SCHED_LOCK(s);
pr->ps_single = NULL;
atomic_clearbits_int(&pr->ps_flags, PS_SINGLEUNWIND | PS_SINGLEEXIT);
- TAILQ_FOREACH(q, &pr->ps_threads, p_thr_link) {
+ SMR_TAILQ_FOREACH_LOCKED(q, &pr->ps_threads, p_thr_link) {
if (q == p || (q->p_flag & P_SUSPSINGLE) == 0)
continue;
atomic_clearbits_int(&q->p_flag, P_SUSPSINGLE);
diff --git sys/kern/kern_synch.c sys/kern/kern_synch.c
index f0338e8f90f..9ef710acf4d 100644
--- sys/kern/kern_synch.c
+++ sys/kern/kern_synch.c
@@ -50,6 +50,7 @@
#include <sys/pool.h>
#include <sys/refcnt.h>
#include <sys/atomic.h>
+#include <sys/smr.h>
#include <sys/witness.h>
#include <sys/tracepoint.h>
@@ -633,7 +634,7 @@ sys_sched_yield(struct proc *p, void *v, register_t *retval)
* can make some progress.
*/
newprio = p->p_usrpri;
- TAILQ_FOREACH(q, &p->p_p->ps_threads, p_thr_link)
+ SMR_TAILQ_FOREACH_LOCKED(q, &p->p_p->ps_threads, p_thr_link)
newprio = max(newprio, q->p_runpri);
setrunqueue(p->p_cpu, p, newprio);
p->p_ru.ru_nvcsw++;
diff --git sys/kern/kern_sysctl.c sys/kern/kern_sysctl.c
index a275fa7b6a9..da4fe6a22cf 100644
--- sys/kern/kern_sysctl.c
+++ sys/kern/kern_sysctl.c
@@ -1596,7 +1596,7 @@ again:
if (!dothreads)
continue;
- TAILQ_FOREACH(p, &pr->ps_threads, p_thr_link) {
+ SMR_TAILQ_FOREACH_LOCKED(p, &pr->ps_threads, p_thr_link) {
if (buflen >= elem_size && elem_count > 0) {
fill_kproc(pr, kproc, p, show_pointers);
error = copyout(kproc, dp, elem_size);
@@ -1696,7 +1696,7 @@ fill_kproc(struct process *pr, struct kinfo_proc *ki,
struct proc *p,
} else {
ki->p_pctcpu = 0;
ki->p_stat = (pr->ps_flags & PS_ZOMBIE) ? SDEAD : SIDL;
- TAILQ_FOREACH(p, &pr->ps_threads, p_thr_link) {
+ SMR_TAILQ_FOREACH_LOCKED(p, &pr->ps_threads, p_thr_link) {
ki->p_pctcpu += p->p_pctcpu;
/* find best state: ONPROC > RUN > STOP > SLEEP > .. */
if (p->p_stat == SONPROC || ki->p_stat == SONPROC)
diff --git sys/kern/subr_witness.c sys/kern/subr_witness.c
index 6ee1619da2b..8e44bd930bc 100644
--- sys/kern/subr_witness.c
+++ sys/kern/subr_witness.c
@@ -1888,7 +1888,7 @@ witness_process_has_locks(struct process *pr)
{
struct proc *p;
- TAILQ_FOREACH(p, &pr->ps_threads, p_thr_link) {
+ SMR_TAILQ_FOREACH_LOCKED(p, &pr->ps_threads, p_thr_link) {
if (witness_thread_has_locks(p))
return (1);
}
@@ -2108,7 +2108,7 @@ db_witness_list_all(db_expr_t addr, int have_addr,
db_expr_t count, char *modif)
LIST_FOREACH(pr, &allprocess, ps_list) {
if (!witness_process_has_locks(pr))
continue;
- TAILQ_FOREACH(p, &pr->ps_threads, p_thr_link) {
+ SMR_TAILQ_FOREACH_LOCKED(p, &pr->ps_threads, p_thr_link) {
if (!witness_thread_has_locks(p))
continue;
db_printf("Process %d (%s) thread %p (%d)\n",
diff --git sys/kern/sys_process.c sys/kern/sys_process.c
index 4f6bc30cd76..1ddf711b2a6 100644
--- sys/kern/sys_process.c
+++ sys/kern/sys_process.c
@@ -301,7 +301,7 @@ ptrace_ctrl(struct proc *p, int req, pid_t pid, caddr_t
addr, int data)
error = ESRCH;
goto fail;
}
- t = TAILQ_FIRST(&tr->ps_threads);
+ t = SMR_TAILQ_FIRST_LOCKED(&tr->ps_threads);
break;
/* calls that accept a PID or a thread ID */
@@ -561,9 +561,9 @@ ptrace_kstate(struct proc *p, int req, pid_t pid, void
*addr)
return ESRCH;
if (t->p_p != tr)
return EINVAL;
- t = TAILQ_NEXT(t, p_thr_link);
+ t = SMR_TAILQ_NEXT_LOCKED(t, p_thr_link);
} else {
- t = TAILQ_FIRST(&tr->ps_threads);
+ t = SMR_TAILQ_FIRST_LOCKED(&tr->ps_threads);
}
if (t == NULL)
@@ -754,7 +754,7 @@ process_tprfind(pid_t tpid, struct proc **tp)
if (tr == NULL)
return NULL;
- *tp = TAILQ_FIRST(&tr->ps_threads);
+ *tp = SMR_TAILQ_FIRST_LOCKED(&tr->ps_threads);
return tr;
}
}
diff --git sys/kern/tty.c sys/kern/tty.c
index efd8bbf5cb9..cdf5b1feca1 100644
--- sys/kern/tty.c
+++ sys/kern/tty.c
@@ -2118,7 +2118,7 @@ process_sum(struct process *pr, fixpt_t *estcpup)
ret = 0;
estcpu = 0;
- TAILQ_FOREACH(p, &pr->ps_threads, p_thr_link) {
+ SMR_TAILQ_FOREACH_LOCKED(p, &pr->ps_threads, p_thr_link) {
if (p->p_stat == SRUN || p->p_stat == SONPROC)
ret = 1;
estcpu += p->p_pctcpu;
@@ -2220,12 +2220,12 @@ update_pickpr:
* - prefer living
* Otherwise take the newest thread
*/
- pick = p = TAILQ_FIRST(&pickpr->ps_threads);
+ pick = p = SMR_TAILQ_FIRST_LOCKED(&pickpr->ps_threads);
if (p == NULL)
goto empty;
run = p->p_stat == SRUN || p->p_stat == SONPROC;
pctcpu = p->p_pctcpu;
- while ((p = TAILQ_NEXT(p, p_thr_link)) != NULL) {
+ while ((p = SMR_TAILQ_NEXT_LOCKED(p, p_thr_link)) != NULL) {
run2 = p->p_stat == SRUN || p->p_stat == SONPROC;
pctcpu2 = p->p_pctcpu;
if (run) {
diff --git sys/sys/proc.h sys/sys/proc.h
index d4ec6450a7a..196e48ce9a6 100644
--- sys/sys/proc.h
+++ sys/sys/proc.h
@@ -50,6 +50,7 @@
#include <sys/resource.h> /* For struct rusage */
#include <sys/rwlock.h> /* For struct rwlock */
#include <sys/sigio.h> /* For struct sigio */
+#include <sys/smr.h>
#ifdef _KERNEL
#include <sys/atomic.h>
@@ -156,6 +157,9 @@ struct unveil;
* R rlimit_lock
* S scheduler lock
* T itimer_mtx
+ *
+ * For SMR related structures that allow lock-free reads, the write lock
+ * is indicated below.
*/
struct process {
/*
@@ -167,7 +171,7 @@ struct process {
struct ucred *ps_ucred; /* Process owner's identity. */
LIST_ENTRY(process) ps_list; /* List of all processes. */
- TAILQ_HEAD(,proc) ps_threads; /* Threads in this process. */
+ SMR_TAILQ_HEAD(,proc) ps_threads; /* [K] Threads in this process. */
LIST_ENTRY(process) ps_pglist; /* List of processes in pgrp. */
struct process *ps_pptr; /* Pointer to parent process. */
@@ -330,16 +334,20 @@ struct p_inentry {
/*
* Locks used to protect struct members in this file:
* I immutable after creation
- * S scheduler lock
+ * K kernel lock
* l read only reference, see lim_read_enter()
* o owned (read/modified only) by this thread
+ * S scheduler lock
+ *
+ * For SMR related structures that allow lock-free reads, the write lock
+ * is indicated below.
*/
struct proc {
TAILQ_ENTRY(proc) p_runq; /* [S] current run/sleep queue */
LIST_ENTRY(proc) p_list; /* List of all threads. */
struct process *p_p; /* [I] The process of this thread. */
- TAILQ_ENTRY(proc) p_thr_link; /* Threads in a process linkage. */
+ SMR_TAILQ_ENTRY(proc) p_thr_link; /* [K] Threads in a process linkage */
TAILQ_ENTRY(proc) p_fut_link; /* Threads in a futex linkage. */
struct futex *p_futex; /* Current sleeping futex. */
@@ -425,8 +433,9 @@ struct proc {
#define SONPROC 7 /* Thread is currently on a CPU. */
#define P_ZOMBIE(p) ((p)->p_stat == SDEAD)
-#define P_HASSIBLING(p) (TAILQ_FIRST(&(p)->p_p->ps_threads) != (p) || \
- TAILQ_NEXT((p), p_thr_link) != NULL)
+#define P_HASSIBLING(p)
\
+ (SMR_TAILQ_FIRST_LOCKED(&(p)->p_p->ps_threads) != (p) || \
+ SMR_TAILQ_NEXT_LOCKED((p), p_thr_link) != NULL)
/*
* These flags are per-thread and kept in p_flag
diff --git sys/uvm/uvm_glue.c sys/uvm/uvm_glue.c
index 390307c4c81..40a10e4c1c5 100644
--- sys/uvm/uvm_glue.c
+++ sys/uvm/uvm_glue.c
@@ -369,7 +369,7 @@ uvm_swapout_threads(void)
* the smallest p_slptime
*/
slpp = NULL;
- TAILQ_FOREACH(p, &pr->ps_threads, p_thr_link) {
+ SMR_TAILQ_FOREACH_LOCKED(p, &pr->ps_threads, p_thr_link) {
switch (p->p_stat) {
case SRUN:
case SONPROC:
