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SubjectRe: [RFC PATCH] timer: Improve itimers scalability
On 08/04, Jason Low wrote:
>
> @@ -973,13 +981,6 @@ static void check_process_timers(struct task_struct *tsk,
> virt_expires = check_timers_list(++timers, firing, utime);
> sched_expires = check_timers_list(++timers, firing, sum_sched_runtime);
>
> - /*
> - * Check for the special case process timers.
> - */
> - check_cpu_itimer(tsk, &sig->it[CPUCLOCK_PROF], &prof_expires, ptime,
> - SIGPROF);
> - check_cpu_itimer(tsk, &sig->it[CPUCLOCK_VIRT], &virt_expires, utime,
> - SIGVTALRM);
> soft = READ_ONCE(sig->rlim[RLIMIT_CPU].rlim_cur);
> if (soft != RLIM_INFINITY) {
> unsigned long psecs = cputime_to_secs(ptime);
> @@ -1010,11 +1011,21 @@ static void check_process_timers(struct task_struct *tsk,
> }
> }
>
> + /*
> + * Check for the special case process timers.
> + */
> + check_cpu_itimer(tsk, &sig->it[CPUCLOCK_PROF], &prof_expires, ptime,
> + SIGPROF);
> + check_cpu_itimer(tsk, &sig->it[CPUCLOCK_VIRT], &virt_expires, utime,
> + SIGVTALRM);
> +

Not sure I understand this part... looks wrong actually, please note
that RLIMIT_CPU block above may need to update prof_expires _after_
check_cpu_itimer(), or I am totally confused.

> if (READ_ONCE(sig->cputimer.running)) {
> struct task_cputime group_sample;
>
> + /*
> + * If another thread in the group is already checking
> + * for the thread group cputimer, then we will skip that.
> + */
> + if (READ_ONCE(sig->cputimer.is_checking_timer))
> + return 0;
> +

Cosmetic, I won't insist, but this is not symmetrical to ->running check,

if (READ_ONCE(sig->cputimer.running) &&
!READ_ONCE(sig->cputimer.is_checking_timer))

looks a littke bit better to me.

Oleg.



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