linux-kernel - Re: [PATCH] timers: consider slack value in mod

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Message-ID: <BANLkTikNSa9otE_cFKRcThUZ5ZCtE7Kyxw@mail.gmail.com>
Date:	Wed, 25 May 2011 16:35:05 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Sebastian Andrzej Siewior <sebastian@...akpoint.cc>
Cc:	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] timers: consider slack value in mod_timer()

On Tue, May 24, 2011 at 8:13 PM, Sebastian Andrzej Siewior
<sebastian@...akpoint.cc> wrote:
> * Yong Zhang | 2011-05-24 15:54:17 [+0800]:
>
>>> diff --git a/kernel/timer.c b/kernel/timer.c
>>> index fd61986..bf09726 100644
>>> --- a/kernel/timer.c
>>> +++ b/kernel/timer.c
>>> @@ -804,6 +804,8 @@ int mod_timer(struct timer_list *timer, unsigned long expires)
>>> ?? ?? ?? ?? ?? ?? ?? ??return 1;
>>>
>>> ?? ?? ?? ??expires = apply_slack(timer, expires);
>>
>>So, why not move above line up, then we can use the recalculated
>>expires?
>
> We leave often before apply_slack() kicks in. From printks() it looks
> like we leave more often in first "return 1" than in the second. Moving
> that line up would lead to more __mode_timer() calls.

Hmmm, so the reason is for a timer whose timer->slack is not set
explicitly. when we recalculate expires, we will get different value
sometimes.

Could you please try the attached patch(webmail will mangle it)

Thanks,
Yong



-- 
Only stand for myself

View attachment "0001-timer-avoid-recount-slack-for-same-expire-pending-ti.patch" of type "text/x-patch" (1936 bytes)