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Date:	Wed, 12 Sep 2007 12:08:45 +0200
From:	Eric Dumazet <>
To:	David Miller <>
Subject: Re: [PATCH] NET : convert IP route cache garbage colleciton from
 softirq processing to a workqueue

On Wed, 12 Sep 2007 02:05:25 -0700 (PDT)
David Miller <> wrote:

> From: Eric Dumazet <>
> Date: Tue, 11 Sep 2007 14:56:13 +0200
> > When the periodic IP route cache flush is done (every 600 seconds on 
> > default configuration), some hosts suffer a lot and eventually trigger
> > the "soft lockup" message.
> > 
> > dst_run_gc() is doing a scan of a possibly huge list of dst_entries,
> > eventually freeing some (less than 1%) of them, while holding the 
> > dst_lock spinlock for the whole scan.
> > 
> > Then it rearms a timer to redo the full thing 1/10 s later...
> > The slowdown can last one minute or so, depending on how active are
> > the tcp sessions.
> > 
> > This second version of the patch converts the processing from a softirq
> > based one to a workqueue.
> > 
> > Even if the list of entries in garbage_list is huge, host is still
> > responsive to softirqs and can make progress.
> > 
> > Instead of reseting gc timer to 0.1 second if one entry was freed in a
> > gc run, we do this if more than 10% of entries were freed.
> I like this patch a lot, some minor fix is needed though:

Thank you

I also spoted a missing static before 
DECLARE_DELAYED_WORK(dst_gc_work, dst_gc_task);
 no need to stress Adrian on this :)

> > +		__builtin_prefetch(&next->next, 1, 0);
> Please use prefetch() instead of a direct explicit
> call to a gcc-specific routine :-)

Unfortunatly, there is no equivalent for this one. 
This gives on my Opterons a nice "prefetchnta"

prefetch(addr) is more like __builtin_prefetch(addr, 0, 3)

I would like to avoid to zap L2 cache with useless data.

__builtin_prefetch() is included from gcc 3.1 (2002), so every 
platform should support it, as linux-2.6 requires gcc 3.2 at least.

I guess you are going to tell me to first publish a patch to lkml :)

Thank you

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