Message-ID: <44172C4C.3020107@watson.ibm.com>
Date: Tue, 14 Mar 2006 15:49:16 -0500
From: Shailabh Nagar <nagar@watson.ibm.com>
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To: Greg KH <greg@kroah.com>
CC: linux-kernel <linux-kernel@vger.kernel.org>,
       Nick Piggin <nickpiggin@yahoo.com.au>
Subject: Re: [Patch 0/9] Per-task delay accounting
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Greg KH wrote:

>On Mon, Mar 13, 2006 at 07:40:34PM -0500, Shailabh Nagar wrote:
>  
>
>>This is the next iteration of the delay accounting patches
>>last posted at
>>	http://www.ussg.iu.edu/hypermail/linux/kernel/0602.3/0893.html
>>    
>>
>
>Do you have any benchmark numbers with this patch applied and with it
>not applied? 
>
None yet. Wanted to iron out the collection/utility aspects a bit before 
going into
the performance impact.

But this seems as good a time as any to collect some stats
using the usual suspects lmbench, kernbench, hackbench etc.

> Last I heard it was a measurable decrease for some
>"important" benchmark results...
>  
>
Might have been from an older iteration where schedstats was fully enabled.
But no point speculating....will run with this set of patches and see 
what shakes out.

One point about the overhead is that it depends on the frequency with 
which data is
collected. So a proper test would probably be a comparison of a 
non-patched kernel
with
a) patches applied but delay accounting not turned on at boot i.e. cost 
of the checks
b) delay accounting turned on but not being read
c) delay accounting turned on and data read for all tasks at some 
"reasonable" rate

Will that be good  ? Other suggestions welcome.

>thanks,
>
>greg k-h
>  
>

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