linux-kernel - Re: [Bug #11308] tbench regression on each kernel release from 2.6.22 -> 2.6.28

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Date:	Fri, 21 Nov 2008 09:51:32 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Christoph Lameter <cl@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [Bug #11308] tbench regression on each kernel release from	2.6.22
 -&gt; 2.6.28

Ingo Molnar a écrit :
> * Christoph Lameter <cl@...ux-foundation.org> wrote:
> 
>> hmmm... Well we are almost there.
>>
>> 2.6.22:
>>
>> Throughput 2526.15 MB/sec 8 procs
>>
>> 2.6.28-rc5:
>>
>> Throughput 2486.2 MB/sec 8 procs
>>
>> 8p Dell 1950 and the number of processors specified on the tbench 
>> command line.
> 
> And with net-next we might even be able to get past that magic limit? 
> net-next is linus-latest plus the latest and greatest networking bits:
> 
>  $ cat .git/config
> 
>  [remote "net-next"]
> 	url = git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next-2.6.git
> 	fetch = +refs/heads/*:refs/remotes/net-next/*
> 
> ... so might be worth a test. Just to satisfy our curiosity and to 
> possibly close the entry :-)
> 

Well, bits in net-next are new stuff for 2.6.29, not really regression fixes,
but yes, they should give nice tbench speedups.


Now, I wish sockets and pipes not going through dcache, not tbench affair
of course but real workloads...

running 8 processes on a 8 way machine doing a 

for (;;)
	close(socket(AF_INET, SOCK_STREAM, 0));

is slow as hell, we hit so many contended cache lines ...

ticket spin locks are slower in this case (dcache_lock for example
is taken twice when we allocate a socket(), once in d_alloc(), another one
in d_instantiate())


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