linux-kernel - Re: [PATCH] SCSI: run queue if SCSI device queue isn't ready and queue is idle

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Date:   Thu, 7 Dec 2017 21:11:54 +0000
From:   Bart Van Assche <Bart.VanAssche@....com>
To:     "ming.lei@...hat.com" <ming.lei@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "hch@...radead.org" <hch@...radead.org>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "axboe@...com" <axboe@...com>, "hare@...e.com" <hare@...e.com>,
        "holger@...lied-asynchrony.com" <holger@...lied-asynchrony.com>,
        "jejb@...ux.vnet.ibm.com" <jejb@...ux.vnet.ibm.com>
Subject: Re: [PATCH] SCSI: run queue if SCSI device queue isn't ready and
 queue is idle

On Thu, 2017-12-07 at 09:31 +0800, Ming Lei wrote:
> But if you always call blk_mq_sched_mark_restart_hctx() before a new
> dispatch, that may affect performance on NVMe which may never trigger
> BLK_STS_RESOURCE.

Hmm ... only the SCSI core implements .get_budget() and .put_budget() and
I proposed to insert a blk_mq_sched_mark_restart_hctx() call under "if
(q->mq_ops->get_budget)". In other words, I proposed to insert a
blk_mq_sched_mark_restart_hctx() call in a code path that is never triggered
by the NVMe driver. So I don't see how the change I proposed could affect
the performance of the NVMe driver?

Bart.