From: Jens Axboe <axboe@kernel.dk>
To: Bart Van Assche <Bart.VanAssche@wdc.com>,
"ming.lei@redhat.com" <ming.lei@redhat.com>
Cc: "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"snitzer@redhat.com" <snitzer@redhat.com>,
"hch@lst.de" <hch@lst.de>,
"martin.petersen@oracle.com" <martin.petersen@oracle.com>,
"hare@suse.de" <hare@suse.de>,
"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
"don.brace@microsemi.com" <don.brace@microsemi.com>,
"james.bottomley@hansenpartnership.com"
<james.bottomley@hansenpartnership.com>,
"osandov@fb.com" <osandov@fb.com>,
"loberman@redhat.com" <loberman@redhat.com>,
"kashyap.desai@broadcom.com" <kashyap.desai@broadcom.com>
Subject: Re: [PATCH 0/3] scsi: scsi-mq: don't hold host_busy in IO path
Date: Fri, 27 Apr 2018 10:19:54 -0600 [thread overview]
Message-ID: <df0f3eb5-b320-91f4-1eab-0aa8b9c836ea@kernel.dk> (raw)
In-Reply-To: <647b4fe833fdf001f724cfa0803c9e3a79d78b13.camel@wdc.com>
On 4/27/18 9:48 AM, Bart Van Assche wrote:
> On Fri, 2018-04-27 at 09:39 -0600, Jens Axboe wrote:
>> blk_mq_tagset_busy_iter(&shost->tag_set, scsi_host_check_in_flight,
>> &in_flight);
>> return in_flight.cnt + atomic_read(&shost->host_busy);
>>
>> The atomic read is basically free, once we get rid of the dirty of that
>> variable on each IO.
>
> Hello Jens,
>
> What makes you think that " + atomic_read(&shost->host_busy)" is necessary?
> I am not aware of any code outside the SCSI core that modifies the host_busy
> member.
It's a (scalable) hack to count those as well. Going forward they should be
converted to just using reserved tags, of course.
--
Jens Axboe
next prev parent reply other threads:[~2018-04-27 16:19 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-20 6:57 [PATCH 0/3] scsi: scsi-mq: don't hold host_busy in IO path Ming Lei
2018-04-20 6:57 ` [PATCH 1/3] scsi: introduce scsi_host_busy() Ming Lei
2018-04-27 15:47 ` Bart Van Assche
2018-04-20 6:57 ` [PATCH 2/3] scsi: read host_busy via scsi_host_busy() Ming Lei
2018-04-27 15:51 ` Bart Van Assche
2018-04-28 8:17 ` Ming Lei
2018-04-20 6:57 ` [PATCH 3/3] scsi: avoid to hold host-wide counter of host_busy for scsi_mq Ming Lei
2018-04-27 16:16 ` Bart Van Assche
2018-04-28 8:26 ` Ming Lei
2018-04-27 15:31 ` [PATCH 0/3] scsi: scsi-mq: don't hold host_busy in IO path Bart Van Assche
2018-04-27 15:39 ` Jens Axboe
2018-04-27 15:48 ` Bart Van Assche
2018-04-27 15:55 ` Laurence Oberman
2018-04-27 16:19 ` Jens Axboe [this message]
2018-04-28 8:47 ` Ming Lei
2018-06-22 15:29 ` Bart Van Assche
2018-06-22 21:43 ` Ming Lei
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