From: Bart Van Assche <Bart.VanAssche@wdc.com>
To: "ming.lei@redhat.com" <ming.lei@redhat.com>
Cc: "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"hch@infradead.org" <hch@infradead.org>,
"jthumshirn@suse.de" <jthumshirn@suse.de>,
"martin.petersen@oracle.com" <martin.petersen@oracle.com>,
"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
"axboe@fb.com" <axboe@fb.com>,
"oleksandr@natalenko.name" <oleksandr@natalenko.name>,
"jejb@linux.vnet.ibm.com" <jejb@linux.vnet.ibm.com>,
"tj@kernel.org" <tj@kernel.org>
Subject: Re: [PATCH V3 7/8] block: allow to allocate req with REQF_PREEMPT when queue is preempt frozen
Date: Tue, 5 Sep 2017 01:40:11 +0000 [thread overview]
Message-ID: <1504575610.3360.7.camel@wdc.com> (raw)
In-Reply-To: <20170904160813.GA21757@ming.t460p>
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WARNING: multiple messages have this Message-ID (diff)
From: Bart Van Assche <Bart.VanAssche@wdc.com>
To: "ming.lei@redhat.com" <ming.lei@redhat.com>
Cc: "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"hch@infradead.org" <hch@infradead.org>,
"jthumshirn@suse.de" <jthumshirn@suse.de>,
"martin.petersen@oracle.com" <martin.petersen@oracle.com>,
"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
"axboe@fb.com" <axboe@fb.com>,
"oleksandr@natalenko.name" <oleksandr@natalenko.name>,
"jejb@linux.vnet.ibm.com" <jejb@linux.vnet.ibm.com>,
"tj@kernel.org" <tj@kernel.org>
Subject: Re: [PATCH V3 7/8] block: allow to allocate req with REQF_PREEMPT when queue is preempt frozen
Date: Tue, 5 Sep 2017 01:40:11 +0000 [thread overview]
Message-ID: <1504575610.3360.7.camel@wdc.com> (raw)
In-Reply-To: <20170904160813.GA21757@ming.t460p>
On Tue, 2017-09-05 at 00:08 +0800, Ming Lei wrote:
> On Mon, Sep 04, 2017 at 03:40:35PM +0000, Bart Van Assche wrote:
> > Have you considered to use the blk-mq "reserved request" mechanism to avoid
> > starvation of power management requests instead of making the block layer
> > even more complicated than it already is?
>
> reserved request is really a bad idea, that means the reserved request
> can't be used for normal I/O, we all know the request/tag space is
> precious, and some device has a quite small tag space, such as sata.
> This way will affect performance definitely.
Sorry but I'm neither convinced that reserving a request for power management
would be a bad idea nor that it would have a significant performance impact nor
that it would be complicated to implement. Have you noticed that the Linux ATA
implementation already reserves a request for internal use and thereby reduces
the queue depth from 32 to 31 (see also ATA_TAG_INTERNAL)? What I would like to
know if is whether the performance impact of reserving a request is more or less
than 1%.
Bart.
next prev parent reply other threads:[~2017-09-05 1:40 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-02 13:08 [PATCH V3 0/8] block/scsi: safe SCSI quiescing Ming Lei
2017-09-02 13:08 ` [PATCH V3 1/8] blk-mq: rename blk_mq_unfreeze_queue as blk_unfreeze_queue Ming Lei
2017-09-02 13:08 ` [PATCH V3 2/8] blk-mq: rename blk_mq_freeze_queue as blk_freeze_queue Ming Lei
2017-09-02 13:08 ` [PATCH V3 3/8] blk-mq: only run hw queues for blk-mq Ming Lei
2017-09-02 13:08 ` [PATCH V3 4/8] blk-mq: rename blk_mq_freeze_queue_wait as blk_freeze_queue_wait Ming Lei
2017-09-02 13:08 ` [PATCH V3 5/8] block: tracking request allocation with q_usage_counter Ming Lei
2017-09-02 13:08 ` [PATCH V3 6/8] block: introduce preempt version of blk_[freeze|unfreeze]_queue Ming Lei
2017-09-04 15:21 ` Bart Van Assche
2017-09-04 15:21 ` Bart Van Assche
2017-09-04 16:20 ` Ming Lei
2017-09-02 13:08 ` [PATCH V3 7/8] block: allow to allocate req with REQF_PREEMPT when queue is preempt frozen Ming Lei
2017-09-02 13:12 ` Ming Lei
2017-09-04 4:13 ` Bart Van Assche
2017-09-04 4:13 ` Bart Van Assche
2017-09-04 7:16 ` Ming Lei
2017-09-04 15:40 ` Bart Van Assche
2017-09-04 15:40 ` Bart Van Assche
2017-09-04 16:08 ` Ming Lei
2017-09-04 16:18 ` Bart Van Assche
2017-09-04 16:18 ` Bart Van Assche
2017-09-04 16:28 ` Ming Lei
2017-09-05 1:40 ` Bart Van Assche [this message]
2017-09-05 1:40 ` Bart Van Assche
2017-09-05 2:23 ` Ming Lei
2017-09-08 3:08 ` Ming Lei
2017-09-08 17:28 ` Bart Van Assche
2017-09-08 17:28 ` Bart Van Assche
2017-09-09 7:21 ` Ming Lei
2017-09-02 13:08 ` [PATCH V3 8/8] SCSI: preempt freeze block queue when SCSI device is put into quiesce Ming Lei
2017-09-02 14:47 ` [PATCH V3 0/8] block/scsi: safe SCSI quiescing Oleksandr Natalenko
2017-09-02 14:47 ` Oleksandr Natalenko
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