linux-kernel - RE: [PATCH] lib/spinlock_debug: Tweak the loop time to fit different

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Date:	Wed, 30 Apr 2014 09:30:55 +0000
From:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	"Wang, Xiaoming" <xiaoming.wang@...el.com>
CC:	"mingo@...hat.com" <mingo@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] lib/spinlock_debug: Tweak the loop time to fit
 different _delay()

Hello Peter,

> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz@...radead.org]
> Sent: Wednesday, April 30, 2014 4:55 PM
> To: Wang, Xiaoming
> Cc: mingo@...hat.com; linux-kernel@...r.kernel.org; Liu, Chuansheng
> Subject: Re: [PATCH] lib/spinlock_debug: Tweak the loop time to fit different
> _delay()
> 
> On Wed, Apr 30, 2014 at 06:40:38PM -0400, Wang, Xiaoming wrote:
> > loops_per_jiffy*Hz  is not always 1 second exactly
> > it depends on the realization of _delay() .
> > delay_tsc is used as _delay() in arch/x86/lib/delay.c
> 
> This just states delay() is broken. The primary response should be to
> try and fix that, no?


delay(1s_count) is accurate, but delay(1) is not accurate indeed, since executing
some instruction, then the 1 cycle delay maybe be used already.

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