linux-block.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Ming Lei <ming.lei@redhat.com>
To: John Garry <john.garry@huawei.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-block@vger.kernel.org, Bart Van Assche <bvanassche@acm.org>,
	Hannes Reinecke <hare@suse.com>, Christoph Hellwig <hch@lst.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Keith Busch <keith.busch@intel.com>
Subject: Re: [PATCH V4 0/5] blk-mq: improvement on handling IO during CPU hotplug
Date: Tue, 22 Oct 2019 08:16:14 +0800	[thread overview]
Message-ID: <20191022001613.GA32193@ming.t460p> (raw)
In-Reply-To: <d4c8e435-b243-4734-6383-3618ad303842@huawei.com>

On Mon, Oct 21, 2019 at 03:02:56PM +0100, John Garry wrote:
> On 21/10/2019 13:53, Ming Lei wrote:
> > On Mon, Oct 21, 2019 at 12:49:53PM +0100, John Garry wrote:
> > > > > > 
> > > > > 
> > > > > Yes, we share tags among all queues, but we generate the tag - known as IPTT
> > > > > - in the LLDD now, as we can no longer use the request tag (as it is not
> > > > > unique per all queues):
> > > > > 
> > > > > https://github.com/hisilicon/kernel-dev/commit/087b95af374be6965583c1673032fb33bc8127e8#diff-f5d8fff19bc539a7387af5230d4e5771R188
> > > > > 
> > > > > As I said, the branch is messy and I did have to fix 087b95af374.
> > > > 
> > > > Firstly this way may waste lots of memory, especially the queue depth is
> > > > big, such as, hisilicon V3's queue depth is 4096.
> > > > 
> > > > Secondly, you have to deal with queue busy efficiently and correctly,
> > > > for example, your real hw tags(IPTT) can be used up easily, and how
> > > > will you handle these dispatched request?
> > > 
> > > I have not seen scenario of exhausted IPTT. And IPTT count is same as SCSI
> > > host.can_queue, so SCSI midlayer should ensure that this does not occur.
> > 
> 
> Hi Ming,
> 
> > That check isn't correct, and each hw queue should have allowed
> > .can_queue in-flight requests.
> 
> There always seems to be some confusion or disagreement on this topic.
> 
> I work according to the comment in scsi_host.h:
> 
> "Note: it is assumed that each hardware queue has a queue depth of
>  can_queue. In other words, the total queue depth per host
>  is nr_hw_queues * can_queue."
> 
> So I set Scsi_host.can_queue = HISI_SAS_MAX_COMMANDS (=4096)

I believe all current drivers set .can_queue as single hw queue's depth.
If you set .can_queue as HISI_SAS_MAX_COMMANDS which is HBA's queue
depth, the hisilicon sas driver will HISI_SAS_MAX_COMMANDS * nr_hw_queues
in-flight requests.

> 
> > 
> > > 
> > > > 
> > > > Finally, you have to evaluate the performance effect, this is highly
> > > > related with how to deal with out-of-IPTT.
> > > 
> > > Some figures from our previous testing:
> > > 
> > > Managed interrupt without exposing multiple queues: 3M IOPs
> > > Managed interrupt with exposing multiple queues: 2.6M IOPs
> > 
> > Then you see the performance regression.
> 
> Let's discuss this when I send the patches, so we don't get sidetracked on
> this blk-mq improvement topic.

OK, what I meant is to use correct driver to test the patches, otherwise
it might be hard to investigate.


Thanks,
Ming


  reply	other threads:[~2019-10-22  0:16 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-14  1:50 Ming Lei
2019-10-14  1:50 ` [PATCH V4 1/5] blk-mq: add new state of BLK_MQ_S_INTERNAL_STOPPED Ming Lei
2019-10-14  1:50 ` [PATCH V4 2/5] blk-mq: prepare for draining IO when hctx's all CPUs are offline Ming Lei
2019-10-14  1:50 ` [PATCH V4 3/5] blk-mq: stop to handle IO and drain IO before hctx becomes dead Ming Lei
2019-11-28  9:29   ` John Garry
2019-10-14  1:50 ` [PATCH V4 4/5] blk-mq: re-submit IO in case that hctx is dead Ming Lei
2019-10-14  1:50 ` [PATCH V4 5/5] blk-mq: handle requests dispatched from IO scheduler " Ming Lei
2019-10-16  8:58 ` [PATCH V4 0/5] blk-mq: improvement on handling IO during CPU hotplug John Garry
2019-10-16 12:07   ` Ming Lei
2019-10-16 16:19     ` John Garry
     [not found]       ` <55a84ea3-647d-0a76-596c-c6c6b2fc1b75@huawei.com>
2019-10-20 10:14         ` Ming Lei
2019-10-21  9:19           ` John Garry
2019-10-21  9:34             ` Ming Lei
2019-10-21  9:47               ` John Garry
2019-10-21 10:24                 ` Ming Lei
2019-10-21 11:49                   ` John Garry
2019-10-21 12:53                     ` Ming Lei
2019-10-21 14:02                       ` John Garry
2019-10-22  0:16                         ` Ming Lei [this message]
2019-10-22 11:19                           ` John Garry
2019-10-22 13:45                             ` Ming Lei
2019-10-25 16:33             ` John Garry
2019-10-28 10:42               ` Ming Lei
2019-10-28 11:55                 ` John Garry
2019-10-29  1:50                   ` Ming Lei
2019-10-29  9:22                     ` John Garry
2019-10-29 10:05                       ` Ming Lei
2019-10-29 17:54                         ` John Garry
2019-10-31 16:28                         ` John Garry
2019-11-28  1:09 ` chenxiang (M)
2019-11-28  2:02   ` Ming Lei
2019-11-28 10:45     ` John Garry

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20191022001613.GA32193@ming.t460p \
    --to=ming.lei@redhat.com \
    --cc=axboe@kernel.dk \
    --cc=bvanassche@acm.org \
    --cc=hare@suse.com \
    --cc=hch@lst.de \
    --cc=john.garry@huawei.com \
    --cc=keith.busch@intel.com \
    --cc=linux-block@vger.kernel.org \
    --cc=tglx@linutronix.de \
    --subject='Re: [PATCH V4 0/5] blk-mq: improvement on handling IO during CPU hotplug' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).