Date: Tue, 2 Nov 2004 14:02:22 -0600
From: Jack Steiner <steiner@sgi.com>
To: Jesse Barnes <jbarnes@engr.sgi.com>
Cc: wli@holomorphy.org, linux-kernel@vger.kernel.org, edwardsg@sgi.com
Subject: Re: contention on profile_lock
Message-ID: <20041102200222.GA5135@sgi.com>
References: <200411021152.16038.jbarnes@engr.sgi.com>
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On Tue, Nov 02, 2004 at 11:52:15AM -0800, Jesse Barnes wrote:
> Hmm, the last patch you sent me worked ok, so I'm not sure why we're seeing 
> problems with profiling now.  There seems to be very heavy contention on 
> profile_lock since profile_hook is called unconditionally every timer tick.  
> Should it only be called if profiling is enabled?  Is there a way we can 
> check the notifier list to see if it's empty before calling it or something?  
> The only user appears to be oprofile timer based profiling, so in the general 
> case we're taking the profile_lock and not doing anything.
> 
> Thanks,
> Jesse

Calling profile_hook() only if the notifier list is non-empty seems like a good
step but I don't think that is the complete fix. We need to be able to
enable profiling without killing performance.


-- 
Thanks

Jack Steiner (steiner@sgi.com)          651-683-5302
Principal Engineer                      SGI - Silicon Graphics, Inc.


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