Message-ID: <45AC2F99.3040209@garzik.org>
Date: Mon, 15 Jan 2007 20:51:21 -0500
From: Jeff Garzik <jeff@garzik.org>
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To: Jens Axboe <jens.axboe@oracle.com>
CC: Robert Hancock <hancockr@shaw.ca>,
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	<B.Steinbrink@gmx.de>,
       linux-kernel@vger.kernel.org, htejun@gmail.com
Subject: Re: SATA exceptions with 2.6.20-rc5
References: <fa.hif5u4ZXua+b0mVNaWEcItWv9i0@ifi.uio.no> <45AAC039.1020808@shaw.ca> <45AAC95B.1020708@garzik.org> <45AAE635.8090308@shaw.ca> <20070115025319.GC4516@kernel.dk> <45AB84D8.3020507@garzik.org> <20070116002336.GB4067@kernel.dk>
In-Reply-To: <20070116002336.GB4067@kernel.dk>
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Jens Axboe wrote:
> On Mon, Jan 15 2007, Jeff Garzik wrote:
>> Jens Axboe wrote:
>>> I'd be surprised if the device would not obey the 7 second timeout rule
>>> that seems to be set in stone and not allow more dirty in-drive cache
>>> than it could flush out in approximately that time.
>> AFAIK Windows flush-cache timeout is 30 seconds, not 7 as with other 
>> commands...
> 
> Ok, 7 seconds for FLUSH_CACHE would have been nice for us too though, as
> it would pretty much guarentee lower latencies for random writes and
> write back caching. The concern is the barrier code, of course. I guess
> I should do some timings on potential worst case patterns some day. Alan
> may have done that sometime in the past, iirc.

FWIW:  According to the drive guys (Eric M, among others), FLUSH CACHE 
will "probably" be under 30 seconds, but pathological cases might even 
extend beyond that.

Definitely more than 7 seconds in less-than-pathological cases, 
unfortunately...

The SCSI layer /should/ already take this (30 second timeout) into 
account, for SYNCHRONIZE CACHE (and thus FLUSH CACHE for libata) but I'm 
too slack to check at the moment.

	Jeff


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