linux-kernel - Re: [PATCH AUTOSEL 5.2 129/249] blk-iolatency: only account submitted bios

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Message-ID: <20190715195806.GA77907@dennisz-mbp>
Date:   Mon, 15 Jul 2019 15:58:06 -0400
From:   Dennis Zhou <dennis@...nel.org>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Dennis Zhou <dennis@...nel.org>,
        Josef Bacik <josef@...icpanda.com>,
        Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 5.2 129/249] blk-iolatency: only account
 submitted bios

On Mon, Jul 15, 2019 at 09:44:54AM -0400, Sasha Levin wrote:
> From: Dennis Zhou <dennis@...nel.org>
> 
> [ Upstream commit a3fb01ba5af066521f3f3421839e501bb2c71805 ]
> 
> As is, iolatency recognizes done_bio and cleanup as ending paths. If a
> request is marked REQ_NOWAIT and fails to get a request, the bio is
> cleaned up via rq_qos_cleanup() and ended in bio_wouldblock_error().
> This results in underflowing the inflight counter. Fix this by only
> accounting bios that were actually submitted.
> 
> Signed-off-by: Dennis Zhou <dennis@...nel.org>
> Cc: Josef Bacik <josef@...icpanda.com>
> Signed-off-by: Jens Axboe <axboe@...nel.dk>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  block/blk-iolatency.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c
> index d22e61bced86..c91b84bb9d0a 100644
> --- a/block/blk-iolatency.c
> +++ b/block/blk-iolatency.c
> @@ -600,6 +600,10 @@ static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio)
>  	if (!blkg || !bio_flagged(bio, BIO_TRACKED))
>  		return;
>  
> +	/* We didn't actually submit this bio, don't account it. */
> +	if (bio->bi_status == BLK_STS_AGAIN)
> +		return;
> +
>  	iolat = blkg_to_lat(bio->bi_blkg);
>  	if (!iolat)
>  		return;
> -- 
> 2.20.1
> 

Hi Sasha,

If you're going to pick this up, c9b3007feca0 ("blk-iolatency: fix
STS_AGAIN handling") fixes this patch, so please pick that up too.

Thanks,
Dennis