From: Mike Snitzer <snitzer@redhat.com>
To: Keith Busch <keith.busch@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>,
dm-devel@redhat.com, shivakrishna.merla@netapp.com,
Bart Van Assche <bvanassche@acm.org>,
jmoyer@redhat.com
Subject: Re: awful request merge results while simulating high IOPS multipath
Date: Wed, 25 Feb 2015 19:11:15 -0500 [thread overview]
Message-ID: <20150226001114.GA22484@redhat.com> (raw)
In-Reply-To: <alpine.LNX.2.00.1502252327150.32385@localhost.lm.intel.com>
On Wed, Feb 25 2015 at 6:57pm -0500,
Keith Busch <keith.busch@intel.com> wrote:
> On Wed, 25 Feb 2015, Mike Snitzer wrote:
> >On Wed, Feb 25 2015 at 1:17pm -0500,
> >Busch, Keith <keith.busch@intel.com> wrote:
> >>Our first bottleneck appears to be the device mapper's single lock
> >>request queue.
> >
> >Obviously if we switched dm-multipath over to blk-mq we'd eliminate
> >that. I'll see how things go and will share any changes I come up
> >with.
>
> Yes, I'm also looking at blk-mq. It appears conversion helps a lot.
Oh, so you've already started a conversion of request-based DM?
> I'm not sure though how many tags or h/w contexts to allocate to ensure
> there's enough but not too many. You can't use the underlying device's
> blk-tagset count (assuming you could even get to it) since those are
> potentially shared among many block devices.
I'm very new to the blk-mq model so I have some learning to do before
I'll be much help.
But there really won't be a one size fits all amount for those resources
will there? A multipath device can have _a lot_ of underlying paths.
next prev parent reply other threads:[~2015-02-26 0:11 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-24 16:44 [PATCH 0/4] dm: simplify request-based DM a bit and an RFC-like perf tweak Mike Snitzer
2015-02-24 16:44 ` [PATCH 1/4] dm: remove unnecessary wrapper around blk_lld_busy Mike Snitzer
2015-02-24 16:44 ` [PATCH 2/4] dm: remove request-based DM queue's lld_busy_fn hook Mike Snitzer
2015-02-24 16:44 ` [PATCH 3/4] dm: remove request-based logic from make_request_fn wrapper Mike Snitzer
2015-02-24 16:44 ` [RFC PATCH 4/4] dm: delay running the queue slightly during request completion Mike Snitzer
2015-02-24 16:51 ` Jens Axboe
2015-02-24 17:22 ` [RFC PATCH 4/4 v2] " Mike Snitzer
2015-02-24 17:52 ` Jens Axboe
2015-02-24 18:12 ` Mike Snitzer
2015-02-24 18:16 ` Jens Axboe
2015-02-24 18:32 ` Mike Snitzer
2015-02-25 0:56 ` awful request merge results while simulating high IOPS multipath Mike Snitzer
2015-02-25 4:14 ` Keith Busch
2015-02-25 15:11 ` Jens Axboe
2015-02-25 18:17 ` Busch, Keith
2015-02-25 22:10 ` Mike Snitzer
2015-02-25 23:57 ` Keith Busch
2015-02-26 0:11 ` Mike Snitzer [this message]
2015-02-26 0:28 ` Keith Busch
2015-02-25 4:38 ` FIXED! [was: awful request merge results while simulating high IOPS] multipath Mike Snitzer
2015-02-25 4:41 ` Mike Snitzer
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