From: Christoph Hellwig <hch@lst.de>
To: Tejun Heo <tj@kernel.org>
Cc: Shaohua Li <shli@fb.com>, Christoph Hellwig <hch@lst.de>,
neilb@suse.de, linux-raid@vger.kernel.org, Kernel-team@fb.com,
dan.j.williams@intel.com,
"Martin K. Petersen" <martin.petersen@oracle.com>,
linux-ide@vger.kernel.org
Subject: Re: raid5-cache I/O path improvements
Date: Wed, 9 Sep 2015 17:59:41 +0200 [thread overview]
Message-ID: <20150909155941.GA28608@lst.de> (raw)
In-Reply-To: <20150908173420.GJ13749@mtj.duckdns.org>
On Tue, Sep 08, 2015 at 01:34:20PM -0400, Tejun Heo wrote:
> Hmmm... grep tells me that dm and md actually are branching on whether
> the underlying device supports FUA. This is tricky. I didn't even
> mean flush_flags to be used directly by upper layers. For rotational
> devices, doing multiple FUAs compared multiple writes followed by
> REQ_FLUSH is probably a lot worse - the head gets moved multiple times
> likely skipping over data which can be written out while traversing
> and it's not like stalling write pipeline and draining write queue has
> much impact on hard drives.
Well, that's what we'd need to do for the raid cache as well, given
the resulst that Shaohua sees. Unless you have a good idea for another
way to handle the issue we'll need to support both behaviors there.
prev parent reply other threads:[~2015-09-09 15:59 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-07 5:20 raid5-cache I/O path improvements Christoph Hellwig
2015-09-07 5:20 ` [PATCH 01/10] raid5-cache: port to 4.3-rc Christoph Hellwig
2015-09-07 5:20 ` [PATCH 02/10] raid5-cache: free I/O units earlier Christoph Hellwig
2015-09-07 5:20 ` [PATCH 03/10] raid5-cache: use FUA writes for the log Christoph Hellwig
2015-09-07 5:20 ` [PATCH 04/10] raid5-cache: clean up r5l_get_meta Christoph Hellwig
2015-09-07 5:20 ` [PATCH 05/10] raid5-cache: refactor bio allocation Christoph Hellwig
2015-09-07 5:20 ` [PATCH 06/10] raid5-cache: take rdev->data_offset into account early on Christoph Hellwig
2015-09-07 5:20 ` [PATCH 07/10] raid5-cache: inline r5l_alloc_io_unit into r5l_new_meta Christoph Hellwig
2015-09-07 5:20 ` [PATCH 08/10] raid5-cache: new helper: r5_reserve_log_entry Christoph Hellwig
2015-09-07 5:20 ` [PATCH 09/10] raid5-cache: small log->seq cleanup Christoph Hellwig
2015-09-07 5:20 ` [PATCH 10/10] raid5-cache: use bio chaining Christoph Hellwig
2015-09-08 0:28 ` raid5-cache I/O path improvements Shaohua Li
2015-09-08 6:12 ` Christoph Hellwig
2015-09-08 15:25 ` Tejun Heo
2015-09-08 15:26 ` Tejun Heo
2015-09-08 15:40 ` Christoph Hellwig
2015-09-08 16:56 ` Shaohua Li
2015-09-08 17:02 ` Tejun Heo
2015-09-08 17:07 ` Shaohua Li
2015-09-08 17:34 ` Tejun Heo
2015-09-09 15:59 ` Christoph Hellwig [this message]
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