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From: Nick Piggin <piggin@cyberone.com.au>
To: Linus Torvalds <torvalds@osdl.org>
Cc: john stultz <johnstul@us.ibm.com>,
	Joel Becker <Joel.Becker@oracle.com>,
	lkml <linux-kernel@vger.kernel.org>,
	Marcelo Tosatti <marcelo.tosatti@cyclades.com>
Subject: Re: get_cycles() on i386
Date: Wed, 05 Nov 2003 14:02:49 +1100	[thread overview]
Message-ID: <3FA86859.8040306@cyberone.com.au> (raw)
In-Reply-To: <3FA86645.7030302@cyberone.com.au>



Nick Piggin wrote:

>
>
> Linus Torvalds wrote:
>
>> On 4 Nov 2003, john stultz wrote:
>>
>>> CONFIG_X86_TSC be the devil. Personally, I'd much prefer dropping the
>>> compile time option and using dynamic detection. Something like (not
>>> recently tested and i believe against 2.5.something, but you get the
>>> idea):
>>>
>>
>> Some of the users are really timing-critical (eg scheduler).
>>
>
> The scheduler uses its own sched_clock which only gives jiffies
> resolution if CONFIG_NUMA is defined. Unfortunate because I think
> its interactive behaviour isn't so good with ms resolution.
>
> The scheduler does not need to have synchronised TSCs though, I think.
> It just means 2 more calls to sched_clock in a slow path (smp migration).
>
Well no, its much trickier than that I think :(




  reply	other threads:[~2003-11-05  3:02 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-11-04 23:22 get_cycles() on i386 Joel Becker
2003-11-04 23:27 ` john stultz
2003-11-04 23:54   ` Linus Torvalds
2003-11-05  2:53     ` Nick Piggin
2003-11-05  3:02       ` Nick Piggin [this message]
2003-11-05 13:35     ` Marcelo Tosatti
2003-12-05 15:55   ` Marcelo Tosatti

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