linux-kernel - Re: [PATCH v2] block: Limit number of items taken from the I/O scheduler in one go

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Message-ID: <20200424064206.GA23666@lst.de>
Date:   Fri, 24 Apr 2020 08:42:06 +0200
From:   Christoph Hellwig <hch@....de>
To:     Salman Qazi <sqazi@...gle.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Ming Lei <ming.lei@...hat.com>,
        Bart Van Assche <bvanassche@....org>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jesse Barnes <jsbarnes@...gle.com>,
        Gwendal Grignou <gwendal@...gle.com>,
        Hannes Reinecke <hare@...e.com>, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2] block: Limit number of items taken from the I/O
 scheduler in one go

On Fri, Apr 24, 2020 at 08:15:29AM +0200, Christoph Hellwig wrote:
> This is a weird loop.  I'd split the code betweem the again label and
> the run_again check here into a __blk_mq_sched_dispatch_requests
> helper, and then you can do:
> 
> 	if (__blk_mq_sched_dispatch_requests()) {
> 		if (__blk_mq_sched_dispatch_requests())
> 			blk_mq_run_hw_queue(hctx, true);
> 	}
> 
> here.  Preferably with ha good comment explaining the logic.

Also I wonder if inverting the return values in the lower level function
would make things a little more readable - a true return suggests
everything worked fine.  Alternative 0 for sucess and -EAGAIN for needs
a retry also would be pretty self-documenting.