* Q: timer_stats_account_xtimer() should reset ->start_site?
[not found] <tip-74019224ac34b044b44a31dd89a54e3477db4896@kernel.org>
@ 2009-02-18 21:09 ` Oleg Nesterov
0 siblings, 0 replies; only message in thread
From: Oleg Nesterov @ 2009-02-18 21:09 UTC (permalink / raw)
To: Ingo Molnar
Cc: hpa, mingo, shemminger, kaber, davem, akpm, tglx, linux-kernel
On 02/18, Ingo Molnar wrote:
>
> +__mod_timer(struct timer_list *timer, unsigned long expires, bool pending_only)
> {
> struct tvec_base *base, *new_base;
> unsigned long flags;
> - int ret = 0;
> + int ret;
> +
> + ret = 0;
>
> timer_stats_timer_set_start_info(timer);
> BUG_ON(!timer->function);
> @@ -603,6 +606,9 @@ int __mod_timer(struct timer_list *timer, unsigned long expires)
> if (timer_pending(timer)) {
> detach_timer(timer, 0);
> ret = 1;
> + } else {
> + if (pending_only)
> + goto out_unlock;
At first glance, I thought this is not exactly right wrt timer stats when
__mod_timer(pending_only => true) fails.
But it turns out, I just can't understand the behaviour of /proc/timer_stats.
The first task which does __mod_timer() fills ->start_site/etc, this info
is cleared by del_timer(). This looks correct.
But when __run_hrtimer/__run_timers report this timer to /proc/timer_stats
we don't clear this info. If the timer expires, and then another task uses
the same timer, timer_stats will report the same ->start_site/pid twice.
Is it correct? Perhaps timer_stats_account_timer() should reset start_site?
Or we can kill the "if (timer->start_site)" in _set_start_info().
Or I missed something. Hmm... and del_timer_sync() doesn't clear start_site.
Confused, please help.
Oleg.
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