From: Jens Axboe <axboe@fb.com>
To: Jeff Moyer <jmoyer@redhat.com>
Cc: <linux-kernel@vger.kernel.org>, <linux-fsdevel@vger.kernel.org>,
<linux-block@vger.kernel.org>
Subject: Re: [PATCH 6/6] writeback: throttle buffered writeback
Date: Tue, 22 Mar 2016 14:19:28 -0600 [thread overview]
Message-ID: <56F1A8D0.4060403@fb.com> (raw)
In-Reply-To: <x49twjyb7cb.fsf@segfault.boston.devel.redhat.com>
On 03/22/2016 02:12 PM, Jeff Moyer wrote:
> Hi, Jens,
>
> Jens Axboe <axboe@fb.com> writes:
>
>> If the device has write back caching, 'wb_cache_delay' delays by
>> this amount of usecs when a write completes before allowing more.
>
> What's the reason behind that?
For classic write back caching, the cache can absorb a bunch of writes
shortly, which means that the completion cost only shows a small part of
the overall cost. This means that if we just throttle on completion,
then when the device starts committing to media, then we'll end up
starving other IO anyway. This knob is a way to attempt to tame that.
--
Jens Axboe
next prev parent reply other threads:[~2016-03-22 20:19 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-22 17:55 [PATCHSET][RFC] Make background writeback not suck Jens Axboe
2016-03-22 17:55 ` [PATCH 1/6] block: ensure we don't truncate top bits of the request command flags Jens Axboe
2016-03-22 18:59 ` Christoph Hellwig
2016-03-22 19:01 ` Jens Axboe
2016-03-25 2:08 ` Mike Christie
2016-03-25 4:18 ` Jens Axboe
2016-03-22 17:55 ` [PATCH 2/6] writeback: wb_start_writeback() should use WB_SYNC_ALL for WB_REASON_SYNC Jens Axboe
2016-03-22 21:34 ` Dave Chinner
2016-03-22 21:40 ` Jens Axboe
2016-03-22 21:51 ` Jens Axboe
2016-03-22 22:04 ` Dave Chinner
2016-03-22 22:07 ` Jens Axboe
2016-03-22 17:55 ` [PATCH 3/6] block: add ability to flag write back caching on a device Jens Axboe
2016-03-22 18:57 ` Christoph Hellwig
2016-03-22 18:59 ` Jens Axboe
2016-03-22 17:55 ` [PATCH 4/6] sd: inform block layer of write cache state Jens Axboe
2016-03-22 17:55 ` [PATCH 5/6] NVMe: " Jens Axboe
2016-03-22 17:55 ` [PATCH 6/6] writeback: throttle buffered writeback Jens Axboe
2016-03-22 20:12 ` Jeff Moyer
2016-03-22 20:19 ` Jens Axboe [this message]
2016-03-22 20:27 ` Jeff Moyer
2016-03-22 21:30 ` Shaohua Li
2016-03-22 21:35 ` Jens Axboe
2016-03-22 21:51 ` [PATCHSET][RFC] Make background writeback not suck Dave Chinner
2016-03-22 22:03 ` Jens Axboe
2016-03-22 22:31 ` Dave Chinner
2016-03-22 22:57 ` Jens Axboe
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