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Date: Wed, 21 Nov 2007 20:49:44 +0100
From: Kris Kennaway <kris@FreeBSD.org>
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To: Alexey Popov <lol@chistydom.ru>
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Cc: Attilio Rao <attilio@freebsd.org>, freebsd-stable@freebsd.org
Subject: Re: 2 x quad-core system is slower that 2 x dual core on FreeBSD
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Alexey Popov wrote:
> Hi.
> 
> Kris Kennaway wrote:
>>> In the meantime there is unfortunately not a lot that can be done, 
>>> AFAICT.  There is one hack that I will send you later but it is not 
>>> likely to help much.  I will also think about how to track down the 
>>> cause of the contention further (the profiling trace only shows that 
>>> it comes mostly from vget/vput but doesn't show where these are 
>>> called from).
>> Actually this patch might help.  It doesn't replace lockmgr but it 
>> does fix a silly thundering herd behaviour.  It probably needs some 
>> adjustment to get it to apply cleanly (it is about 7 months old), and 
>> I apparently stopped using it because I ran into deadlocks.  It might 
>> be stable enough to at least see how much it helps.
> Sorry, I didn't try you patch yet but I have other news.
> 
> As mentioned in the description of your patch there is probably a 
> scalability problem with stat() syscall on FreeBSD.

Not as such, that was just a random example I chose to illustrate the 
lockmgr problems I described earlier.

Try the patch I posted, it should help.

Kris