From: Bart Van Assche <Bart.VanAssche@wdc.com>
To: "ming.lei@redhat.com" <ming.lei@redhat.com>,
"axboe@kernel.dk" <axboe@kernel.dk>
Cc: Bart Van Assche <Bart.VanAssche@wdc.com>,
"hch@infradead.org" <hch@infradead.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"sagi@grimberg.me" <sagi@grimberg.me>
Subject: Re: [PATCH 4/6] blk-mq: use EWMA to estimate congestion threshold
Date: Wed, 12 Jul 2017 15:39:14 +0000 [thread overview]
Message-ID: <1499873952.2554.5.camel@wdc.com> (raw)
In-Reply-To: <20170712023028.GB13036@ming.t460p>
On Wed, 2017-07-12 at 10:30 +0800, Ming Lei wrote:
> On Tue, Jul 11, 2017 at 12:25:16PM -0600, Jens Axboe wrote:
> > What happens with fluid congestion boundaries, with shared tags?
>=20
> The approach in this patch should work, but the threshold may not
> be accurate in this way, one simple method is to use the average
> tag weight in EWMA, like this:
>=20
> sbitmap_weight() / hctx->tags->active_queues
Hello Ming,
That approach would result in a severe performance degradation. "active_que=
ues"
namely represents the number of queues against which I/O ever has been queu=
ed.
If e.g. 64 LUNs would be associated with a single SCSI host and all 64 LUNs=
are
responding and if the queue depth would also be 64 then the approach you
proposed will reduce the effective queue depth per LUN from 64 to 1.
Bart.=
next prev parent reply other threads:[~2017-07-12 15:39 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-11 18:20 [PATCH 0/6] blk-mq: introduce congestion control Ming Lei
2017-07-11 18:20 ` [PATCH 1/6] xen-blkfront: avoid to use start/stop queue Ming Lei
2017-07-11 18:41 ` Konrad Rzeszutek Wilk
2017-07-12 2:52 ` Ming Lei
2017-07-11 18:41 ` Bart Van Assche
2017-07-12 2:59 ` Ming Lei
2017-07-12 3:05 ` Ming Lei
2017-07-11 21:24 ` Roger Pau Monné
2017-07-12 3:12 ` Ming Lei
2017-07-11 18:20 ` [PATCH 2/6] SCSI: use blk_mq_run_hw_queues() in scsi_kick_queue() Ming Lei
2017-07-11 19:57 ` Bart Van Assche
2017-07-12 3:15 ` Ming Lei
2017-07-12 15:12 ` Bart Van Assche
2017-07-13 10:23 ` Ming Lei
2017-07-13 17:44 ` Bart Van Assche
2017-07-11 18:21 ` [PATCH 3/6] blk-mq: send the request to dispatch list if direct issue returns busy Ming Lei
2017-07-11 20:18 ` Bart Van Assche
2017-07-12 3:45 ` Ming Lei
2017-07-11 18:21 ` [PATCH 4/6] blk-mq: use EWMA to estimate congestion threshold Ming Lei
2017-07-11 18:25 ` Jens Axboe
2017-07-12 2:30 ` Ming Lei
2017-07-12 15:39 ` Bart Van Assche [this message]
2017-07-13 10:43 ` Ming Lei
2017-07-13 14:56 ` Bart Van Assche
2017-07-13 15:32 ` Ming Lei
2017-07-13 17:35 ` Bart Van Assche
2017-07-11 18:39 ` Jens Axboe
2017-07-12 3:20 ` Ming Lei
2017-07-11 21:02 ` Bart Van Assche
2017-07-12 3:43 ` Ming Lei
2017-07-11 18:21 ` [PATCH 5/6] blk-mq: introduce basic congestion control Ming Lei
2017-07-11 18:21 ` [PATCH 6/6] blk-mq: unexport APIs for start/stop queues Ming Lei
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