From: Neil Brown <neilb@suse.de>
To: Shaohua Li <shli@fb.com>, Christoph Hellwig <hch@lst.de>
Cc: "linux-raid@vger.kernel.org" <linux-raid@vger.kernel.org>,
Kernel Team <Kernel-team@fb.com>,
"dan.j.williams@intel.com" <dan.j.williams@intel.com>
Subject: Re: raid5-cache I/O path improvements V2
Date: Tue, 15 Sep 2015 09:23:44 +0200 [thread overview]
Message-ID: <87a8so6t8f.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <D21C6812.74CB%shli@fb.com>
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Shaohua Li <shli@fb.com> writes:
> On 9/11/15, 11:17 PM, "Christoph Hellwig" <hch@lst.de> wrote:
>
>>Hi Shaohua, hi Neil,
>>
>>this series contains a few updates to the raid5-cache feature.
>>
>>The first patch just ports it to the post-4.2 block layer. As part of
>>that
>>I noticed that it currently doesn't handle I/O errors - fixes for that
>>will
>>follow.
>>
>>The second and third patch simplify the I/O unit state machine and reduce
>>latency and memory usage for the I/O units. The remainder are just a
>>couple
>>of cleanups in this area that I stumbled upon.
>>
>>Changes since V1:
>> - only use REQ_FUA if supported natively by the log device
>
> Hi Christoph,
>
> I finally got some data with a Samsung SSD, which supports fua. Controller
> is ahci.
> Test is a simple fio with all full stripe write.
>
> libata.fua=0, throughput 247m/s
> libata.fua=1, throughput 74m/s
Eek! That's a big price to pay!
>
> fua is significantly slower. I think we need a sysfs config to enable fua.
I don't want a sysfs config if we can possibly avoid it.
Christoph's code sets FUA on every block written to the log, both data
and metadata. Is that really what we want?
I don't know much of the hardware details, but wouldn't setting FUA and
FLUSH on the last block written be just as effective and possibly faster
(by giving more flexibility to lower layers)??
NeilBrown
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next prev parent reply other threads:[~2015-09-15 7:23 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-12 6:17 raid5-cache I/O path improvements V2 Christoph Hellwig
2015-09-12 6:17 ` [PATCH 01/12] raid5-cache: port to 4.3-rc Christoph Hellwig
2015-09-12 6:17 ` [PATCH 02/12] raid5-cache: free I/O units earlier Christoph Hellwig
2015-09-15 7:00 ` Neil Brown
2015-09-17 1:50 ` Christoph Hellwig
2015-09-15 8:07 ` Neil Brown
2015-09-17 1:48 ` Christoph Hellwig
2015-09-12 6:17 ` [PATCH 03/12] raid5-cache: rename flushed_ios to finished_ios Christoph Hellwig
2015-09-12 6:17 ` [PATCH 04/12] raid5-cache: factor out a helper to run all stripes for an I/O unit Christoph Hellwig
2015-09-12 6:17 ` [PATCH 05/12] raid5-cache: use FUA writes for the log Christoph Hellwig
2015-09-12 6:17 ` [PATCH 06/12] raid5-cache: clean up r5l_get_meta Christoph Hellwig
2015-09-12 6:17 ` [PATCH 07/12] raid5-cache: refactor bio allocation Christoph Hellwig
2015-09-12 6:17 ` [PATCH 08/12] raid5-cache: take rdev->data_offset into account early on Christoph Hellwig
2015-09-12 6:17 ` [PATCH 09/12] raid5-cache: inline r5l_alloc_io_unit into r5l_new_meta Christoph Hellwig
2015-09-12 6:17 ` [PATCH 10/12] raid5-cache: new helper: r5_reserve_log_entry Christoph Hellwig
2015-09-12 6:17 ` [PATCH 11/12] raid5-cache: small log->seq cleanup Christoph Hellwig
2015-09-12 6:17 ` [PATCH 12/12] raid5-cache: use bio chaining Christoph Hellwig
2015-09-14 19:11 ` raid5-cache I/O path improvements V2 Shaohua Li
2015-09-15 7:23 ` Neil Brown [this message]
2015-09-15 21:54 ` Shaohua Li
2015-09-17 1:53 ` Christoph Hellwig
2015-09-28 14:01 ` Christoph Hellwig
2015-09-30 5:39 ` Neil Brown
2015-09-30 15:00 ` Christoph Hellwig
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