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List:       linux-scsi
Subject:    Re: [RFC] relaxed barrier semantics
From:       Hannes Reinecke <hare () suse ! de>
Date:       2010-08-06 14:56:56
Message-ID: 4C5C22B8.9040109 () suse ! de
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Vladislav Bolkhovitin wrote:
> Christoph Hellwig, on 08/05/2010 11:50 PM wrote:
>> On Thu, Aug 05, 2010 at 11:48:19PM +0400, Vladislav Bolkhovitin wrote:
>>> So, I believe, Linux must use that possibility to get full storage
>>> performance and to finally simplify its storage stack.
>>
>> So instead of talking what about doing a prototype and show us what
>> improvement it gives?
> 
> Sure, I'd love to. But, unfortunately, I can't clone myself, so I'm
> trying to help the best of what I could: my level of storage and SCSI
> expertise. This area is quite special, so I'm trying to explain some
> misunderstandings I see and illustrate my points by some possible work
> flows and interfaces.
> 
I can't, neither.

But I can do bonnie runs in no time.
I have done some preliminary benchmarks by just enable ordered
queueing in sd.c and no other changes.
Bonnie says:

Writing intelligently: 115208 vs.  82739 
Reading intelligently: 134133 vs. 129395

putc() performance suffers, though:
I get 52M vs 90M writing and 50M vs. 65M reading.
No idea why; shouldn't be that harmful here.

But in any case there is some speed improvement
to be had from using ordered tags.

Oh, and that was against an EVA 6400.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Markus Rex, HRB 16746 (AG Nürnberg)
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