linux-kernel - Re: [PATCH (block.git) 0/2] IO CPU affinity update:

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Message-ID: <47DEDB3F.3040500@hp.com>
Date:	Mon, 17 Mar 2008 16:57:35 -0400
From:	"Alan D. Brunelle" <Alan.Brunelle@...com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	linux-kernel@...r.kernel.org, npiggin@...e.de, dgc@....com
Subject: Re: [PATCH (block.git) 0/2] IO CPU affinity update:

Jens Axboe wrote:
> On Mon, Mar 17 2008, Alan D. Brunelle wrote:
>> Hi Jens -
>>
>> Two patches: 
>>
>> 1. Adds in the IRQ saving to generic_smp_call_function_single_interrupt (as you had suggested).
>> 2. Ensures a single IPI generated to get a remote function call handler going. 
>>
>> So far it is working better than before on the 4-way IA64 w/ the mkfs/untar/make test suite - after 22 runs:
>>
>> Part  RQ   MIN     AVG     MAX      Dev
>> ----- --  ------  ------  ------  ------
>>  mkfs  0  18.786  19.253  19.655   0.241
>>  mkfs  1  18.639  19.182  19.786   0.293
>>
>> untar  0  17.140  17.486  18.250   0.322
>> untar  1  16.951  17.494  18.274   0.350
>>
>>  make  0  22.927  24.310  34.339   2.287
>>  make  1  22.863  23.788  24.189   0.333
>>
>>  comb  0  59.478  61.049  70.320   2.142
>>  comb  1  59.875  60.463  61.305   0.458
>>
>>  psys  0   3.96%   4.14%   4.39%   0.100
>>  psys  1   3.60%   3.85%   4.19%   0.176
>>
>> So we're seeing reduced time (~1.0%) and reduced %sys to do it (7.0%).
>> The tighter deviations for make with rq=1 may be interesting... :-)
>>
>> I've compiled & booted the patches for x86_64 - rq=1 is working on
>> that platform too.
> 
> This is starting to look pretty good! Thanks a lot for these results,
> and the ->activated optimizations. I had a feeling the unstable results
> were something like this, missing ipi's.
> 

Jens: FYI: I am still seeing infrequent hangs on the x86_64-based platform. It happened again today after my patch was added, I did get <alt><sysrq><W> to work this time, and the threads that were stuck were waiting for IOs to complete. I believe at some point you were thinking of hacking in a block IO dump magic key as well - is that there yet?

I'll get to the ia64 testing tomorrow - have to run now, spent most of the day looking at what could cause stuff to be missed on x86_64. The code looks solid to me, but this hang needs to be figured out. 

Lastly, I did do a run on a 16-way ia64 (with my patches) and again it ran fine.

Alan
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