From: Jeff Moyer <jmoyer@redhat.com>
To: Jens Axboe <axboe@fb.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 16:27:29 -0400 [thread overview]
Message-ID: <x49poumb6mm.fsf@segfault.boston.devel.redhat.com> (raw)
In-Reply-To: <56F1A8D0.4060403@fb.com> (Jens Axboe's message of "Tue, 22 Mar 2016 14:19:28 -0600")
Jens Axboe <axboe@fb.com> writes:
> 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.
Ah, makes perfect sense. Thanks!
-Jeff
next prev parent reply other threads:[~2016-03-22 20:27 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
2016-03-22 20:27 ` Jeff Moyer [this message]
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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