From: "Martin K. Petersen" <martin.petersen@oracle.com>
To: Christof Schmitt <christof.schmitt@de.ibm.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>,
Jens Axboe <axboe@kernel.dk>,
linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [patch 0/1] Apply segment size and segment boundary to integrity data
Date: Wed, 21 Jul 2010 00:20:01 -0400 [thread overview]
Message-ID: <yq1y6d579fy.fsf@sermon.lab.mkp.net> (raw)
In-Reply-To: <20100720092850.GA4547@schmichrtp.mainz.de.ibm.com> (Christof Schmitt's message of "Tue, 20 Jul 2010 11:28:50 +0200")
>>>>> "Christof" == Christof Schmitt <christof.schmitt@de.ibm.com> writes:
Christof> To have a simple approach that covers the case with one
Christof> integrity data segment per user data segment, we only report
Christof> half the size for the scatterlist length when running
Christof> DIX. This guarantees that the other half can be used for
Christof> integrity data.
Yup, a few of our partners did something similar.
My concern is the scenario where we submit lots of 512-byte writes that
get merged into (in your case) 4 KB segments. Each of those 512-byte
writes could come with an 8-byte integrity metadata tuple. And so you'd
need 8 DI scatterlist elements per data element.
Christof> Meaning the integrity data sg list would have more entries
Christof> than max_segments? I have not seen this during my experiments,
Christof> but then i likely have not hit every case of a possible
Christof> request layout.
dd to the block device is usually a good way to issue long scatterlists.
Christof> Ok, i have to look into that as well. It would be an issue
Christof> with the approach we are looking at now: If there are
Christof> max_segments data segments, and more than max_segments
Christof> integrity data segments, we will overrun the hardware
Christof> constraint.
Ok.
--
Martin K. Petersen Oracle Linux Engineering
next prev parent reply other threads:[~2010-07-21 4:21 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-07-15 15:34 [patch 0/1] Apply segment size and segment boundary to integrity data Christof Schmitt
2010-07-15 15:34 ` [patch 1/1] block: Apply segment size and boundary limits " Christof Schmitt
2010-07-15 15:53 ` Jens Axboe
2010-07-15 16:03 ` [patch 0/1] Apply segment size and segment boundary " Martin K. Petersen
2010-07-15 16:14 ` Jens Axboe
2010-07-15 16:35 ` Martin K. Petersen
2010-07-15 16:40 ` Jens Axboe
2010-07-16 8:30 ` Christof Schmitt
2010-07-20 4:45 ` Martin K. Petersen
2010-07-20 9:28 ` Christof Schmitt
2010-07-21 4:20 ` Martin K. Petersen [this message]
2010-08-02 11:05 ` Christof Schmitt
2010-08-03 4:44 ` Martin K. Petersen
2010-08-11 8:07 ` Christof Schmitt
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