From: Jeff Garzik <jeff@garzik.org>
To: Lars Ellenberg <Lars.Ellenberg@linbit.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Neil Brown <neilb@cse.unsw.edu.au>,
linux-raid@vger.kernel.org, Andrew Morton <akpm@osdl.org>,
Jens Axboe <axboe@suse.de>
Subject: Re: [patch] latency problem in md driver
Date: Fri, 22 Dec 2006 10:19:53 -0500 [thread overview]
Message-ID: <458BF799.6010703@garzik.org> (raw)
In-Reply-To: <20061222143215.GD7477@soda.linbit>
Lars Ellenberg wrote:
> md raidX make_request functions strip off the BIO_RW_SYNC flag,
> this introducing additional latency.
>
> below is a suggested patch for the raid1.c .
> other suggested solutions would be to let the bio_clone do its work,
> and not reassign thereby stripping off all flags.
> at most strip off known unwanted flags (the BARRIER flag).
It sounds like a major bug to strip the barrier flag. I quite
understand that a barrier to a RAID device as a whole behaves
differently from a barrier to an ATA or SCSI device, but that's no
excuse to avoid the problem.
If MD does not pass barriers, it is unilaterally dropping the "data made
it to the media" guarantee.
Jeff
next prev parent reply other threads:[~2006-12-22 15:19 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-12-22 14:32 [patch] latency problem in md driver Lars Ellenberg
2006-12-22 15:19 ` Jeff Garzik [this message]
2006-12-22 15:37 ` Ric Wheeler
2006-12-22 15:40 ` Lars Ellenberg
2006-12-22 17:33 ` Lars Ellenberg
2006-12-22 20:40 ` Neil Brown
2006-12-26 13:09 ` Lars Ellenberg
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