From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Fri, 10 Nov 2017 09:29:57 -0800 From: Christoph Hellwig To: Jens Axboe Cc: "linux-block@vger.kernel.org" Subject: Re: [PATCH] blk-mq: only run the hardware queue if IO is pending Message-ID: <20171110172957.GA29446@infradead.org> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: List-ID: On Fri, Nov 10, 2017 at 09:12:18AM -0700, Jens Axboe wrote: > Currently we are inconsistent in when we decide to run the queue. Using > blk_mq_run_hw_queues() we check if the hctx has pending IO before > running it, but we don't do that from the individual queue run function, > blk_mq_run_hw_queue(). This results in a lot of extra and pointless > queue runs, potentially, on flush requests and (much worse) on tag > starvation situations. This is observable just looking at the top > output, with lots of kworkers active. For the !async runs, it just adds > to the CPU overhead of blk-mq. > > Move the has-pending check into the run function instead of having > callers do it. > > Signed-off-by: Jens Axboe Do we even still need the blk_mq_hctx_has_pending helper at all? Except for that this looks fine to me: Reviewed-by: Christoph Hellwig