linux-kernel - Re: SMP performance degradation with sysbench

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Date:	Tue, 27 Feb 2007 00:41:30 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Nick Piggin <nickpiggin@...oo.com.au>
CC:	Rik van Riel <riel@...hat.com>,
	Lorenzo Allegrucci <l_allegrucci@...oo.it>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: SMP performance degradation with sysbench

Nick Piggin wrote:
> Rik van Riel wrote:
> 
>> Lorenzo Allegrucci wrote:
>>
>>> Hi lkml,
>>>
>>> according to the test below (sysbench) Linux seems to have scalability
>>> problems beyond 8 client threads:
>>> http://jeffr-tech.livejournal.com/6268.html#cutid1
>>> http://jeffr-tech.livejournal.com/5705.html
>>> Hardware is an 8-core amd64 system and jeffr seems willing to try more
>>> Linux versions on that machine.
>>> Anyway, is there anyone who can reproduce this?
>>
>>
>>
>> I have reproduced it on a quad core test system.
>>
>> With 4 threads (on 4 cores) I get a high throughput, with
>> approximately 58% user time and 42% system time.
>>
>> With 8 threads (on 4 cores) I get way lower throughput,
>> with 37% user time, 29% system time 35% idle time!
>>
>> The maximum time taken per query also increases from
>> 0.0096s to 0.5273s. Ouch!
>>
>> I don't know if this is MySQL, glibc or Linux kernel,
>> but something strange is going on...
> 
> 
> Like you, I'm also seeing idle time start going up as threads increase.
> 
> I initially thought this was a problem with the multiprocessor scheduler,
> because the pattern is exactly like some artificat in the load balancing.

"artificat"

Wow. I must need some sleep :) Please excuse any other typos!

-- 
SUSE Labs, Novell Inc.
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