From: Jens Axboe <axboe@fb.com>
To: Keith Busch <keith.busch@intel.com>
Cc: "Matias Bjørling" <m@bjorling.me>,
"Matthew Wilcox" <willy@linux.intel.com>,
"sbradshaw@micron.com" <sbradshaw@micron.com>,
"tom.leiming@gmail.com" <tom.leiming@gmail.com>,
"hch@infradead.org" <hch@infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>
Subject: Re: [PATCH v7] NVMe: conversion to blk-mq
Date: Fri, 13 Jun 2014 08:07:29 -0600 [thread overview]
Message-ID: <539B05A1.7080700@fb.com> (raw)
In-Reply-To: <alpine.LRH.2.03.1406121757130.4699@AMR>
On 06/12/2014 06:06 PM, Keith Busch wrote:
> When cancelling IOs, we have to check if the hwctx has a valid tags
> for some reason. I have 32 cores in my system and as many queues, but
It's because unused queues are torn down, to save memory.
> blk-mq is only using half of those queues and freed the "tags" for the
> rest after they'd been initialized without telling the driver. Why is
> blk-mq not making utilizing all my queues?
You have 31 + 1 queues, so only 31 mappable queues. blk-mq symmetrically
distributes these, so you should have a core + thread sibling on 16
queues. And yes, that leaves 15 idle hardware queues for this specific
case. I like the symmetry, it makes it more predictable if things are
spread out evenly.
But it is a policy decision that could be changed. The logic is in the
50 lines of code in block/blk-mq-cpumap.c:blk_mq_update_queue_map().
Thanks for the abort and completion fixes, looks a lot better now. It
might be cleaner to have blk_mq_tag_busy_iter() just work for
!hctx->tags, since this is actually the 2nd time I've run into this now.
next prev parent reply other threads:[~2014-06-13 14:08 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-10 9:20 [PATCH v7] conversion to blk-mq Matias Bjørling
2014-06-10 9:20 ` [PATCH v7] NVMe: " Matias Bjørling
2014-06-10 15:51 ` Keith Busch
2014-06-10 16:19 ` Jens Axboe
2014-06-10 19:29 ` Keith Busch
2014-06-10 19:58 ` Jens Axboe
2014-06-10 21:10 ` Keith Busch
2014-06-10 21:14 ` Jens Axboe
2014-06-10 21:21 ` Keith Busch
2014-06-10 21:33 ` Matthew Wilcox
2014-06-11 16:54 ` Jens Axboe
2014-06-11 17:09 ` Matthew Wilcox
2014-06-11 22:22 ` Matias Bjørling
2014-06-11 22:51 ` Keith Busch
2014-06-12 14:32 ` Matias Bjørling
2014-06-12 16:24 ` Keith Busch
2014-06-13 0:06 ` Keith Busch
2014-06-13 14:07 ` Jens Axboe [this message]
2014-06-13 15:05 ` Keith Busch
2014-06-13 15:11 ` Jens Axboe
2014-06-13 15:16 ` Keith Busch
2014-06-13 18:14 ` Jens Axboe
2014-06-13 19:22 ` Keith Busch
2014-06-13 19:29 ` Jens Axboe
2014-06-13 20:56 ` Jens Axboe
2014-06-13 21:28 ` Jens Axboe
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