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authorLinus Torvalds <torvalds@linux-foundation.org>2022-03-24 10:16:00 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2022-03-24 10:16:00 -0700
commitcd4699c5fd66b00211f4709b9957bfd7b0a02ddc (patch)
treebe9c279ca9597a9da17e649a521f60591fe4d103 /kernel/time
parent2e2d4650b34ffe0a39f70acc9429a58d94e39236 (diff)
parent18c91bb2d87268d23868bf13508f5bc9cf04e89a (diff)
Merge tag 'prlimit-tasklist_lock-for-v5.18' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace
Pull tasklist_lock optimizations from Eric Biederman: "prlimit and getpriority tasklist_lock optimizations The tasklist_lock popped up as a scalability bottleneck on some testing workloads. The readlocks in do_prlimit and set/getpriority are not necessary in all cases. Based on a cycles profile, it looked like ~87% of the time was spent in the kernel, ~42% of which was just trying to get *some* spinlock (queued_spin_lock_slowpath, not necessarily the tasklist_lock). The big offenders (with rough percentages in cycles of the overall trace): - do_wait 11% - setpriority 8% (done previously in commit 7f8ca0edfe07) - kill 8% - do_exit 5% - clone 3% - prlimit64 2% (this patchset) - getrlimit 1% (this patchset) I can't easily test this patchset on the original workload for various reasons. Instead, I used the microbenchmark below to at least verify there was some improvement. This patchset had a 28% speedup (12% from baseline to set/getprio, then another 14% for prlimit). This series used to do the setpriority case, but an almost identical change was merged as commit 7f8ca0edfe07 ("kernel/sys.c: only take tasklist_lock for get/setpriority(PRIO_PGRP)") so that has been dropped from here. One interesting thing is that my libc's getrlimit() was calling prlimit64, so hoisting the read_lock(tasklist_lock) into sys_prlimit64 had no effect - it essentially optimized the older syscalls only. I didn't do that in this patchset, but figured I'd mention it since it was an option from the previous patch's discussion" micobenchmark.c: --------------- int main(int argc, char **argv) { pid_t child; struct rlimit rlim[1]; fork(); fork(); fork(); fork(); fork(); fork(); for (int i = 0; i < 5000; i++) { child = fork(); if (child < 0) exit(1); if (child > 0) { usleep(1000); kill(child, SIGTERM); waitpid(child, NULL, 0); } else { for (;;) { setpriority(PRIO_PROCESS, 0, getpriority(PRIO_PROCESS, 0)); getrlimit(RLIMIT_CPU, rlim); } } } return 0; } Link: https://lore.kernel.org/lkml/20211213220401.1039578-1-brho@google.com/ [v1] Link: https://lore.kernel.org/lkml/20220105212828.197013-1-brho@google.com/ [v2] Link: https://lore.kernel.org/lkml/20220106172041.522167-1-brho@google.com/ [v3] * tag 'prlimit-tasklist_lock-for-v5.18' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: prlimit: do not grab the tasklist_lock prlimit: make do_prlimit() static
Diffstat (limited to 'kernel/time')
-rw-r--r--kernel/time/posix-cpu-timers.c12
1 files changed, 9 insertions, 3 deletions
diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 96b4e7810426..e13e628509fb 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -34,14 +34,20 @@ void posix_cputimers_group_init(struct posix_cputimers *pct, u64 cpu_limit)
* tsk->signal->posix_cputimers.bases[clock].nextevt expiration cache if
* necessary. Needs siglock protection since other code may update the
* expiration cache as well.
+ *
+ * Returns 0 on success, -ESRCH on failure. Can fail if the task is exiting and
+ * we cannot lock_task_sighand. Cannot fail if task is current.
*/
-void update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new)
+int update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new)
{
u64 nsecs = rlim_new * NSEC_PER_SEC;
+ unsigned long irq_fl;
- spin_lock_irq(&task->sighand->siglock);
+ if (!lock_task_sighand(task, &irq_fl))
+ return -ESRCH;
set_process_cpu_timer(task, CPUCLOCK_PROF, &nsecs, NULL);
- spin_unlock_irq(&task->sighand->siglock);
+ unlock_task_sighand(task, &irq_fl);
+ return 0;
}
/*