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Message-ID: <4379FC75.80704@watson.ibm.com>
Date: Tue, 15 Nov 2005 10:19:17 -0500
From: Shailabh Nagar <nagar@watson.ibm.com>
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To: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
CC: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org,
       Ingo Molnar <mingo@elte.hu>
Subject: Re: [Patch 1/4] Delay accounting: Initialization
References: <43796596.2010908@watson.ibm.com> <20051114202017.6f8c0327.akpm@osdl.org> <20051115064954.GB31904@logos.cnet>
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Marcelo Tosatti wrote:
> On Mon, Nov 14, 2005 at 08:20:17PM -0800, Andrew Morton wrote:
> 
>>Shailabh Nagar <nagar@watson.ibm.com> wrote:
>>
>>>+	*ts = sched_clock();
>>
>>I'm not sure that it's kosher to use sched_clock() for fine-grained
>>timestamping like this.  Ingo had issues with it last time this happened?  
> 
> 
> If the system boots with use_rtc == 0 you're going to get jiffies based
> resolution from sched_clock(). I have a 1GHz Pentium 3 around here which
> does that.

Good point, thanks. This reemphasizes the need for better normalization
at output time.

> Maybe use do_gettimeofday() for such systems?

Perhaps getnstimeofday() so resolution isn't reduced to msec level unnecessarily.
In these patches, userspace takes responsibility for handling wraparound so
delivering a reasonably high-resolution delay data from the kernel is preferable.

> 
> Would be nice to have a sort of per-arch overridable "gettime()" function?
> 

Provided as part of this patch ?


>><too lazy to read all the code> Do you normalise these numbers in some
>>manner before presenting them to userspace?  If so, by what means?



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