From: Mike Galbraith <efault@gmx.de>
To: Jens Axboe <axboe@kernel.dk>, Paolo Valente <paolo.valente@linaro.org>
Cc: Christoph Hellwig <hch@lst.de>,
linux-block <linux-block@vger.kernel.org>,
Ulf Hansson <ulf.hansson@linaro.org>,
LKML <linux-kernel@vger.kernel.org>,
Linus Walleij <linus.walleij@linaro.org>,
Oleksandr Natalenko <oleksandr@natalenko.name>
Subject: Re: bug in tag handling in blk-mq?
Date: Wed, 09 May 2018 06:11:29 +0200 [thread overview]
Message-ID: <1525839089.15732.1.camel@gmx.de> (raw)
In-Reply-To: <57952405-bdeb-f4e4-1aef-a7c0a8a68674@kernel.dk>
On Tue, 2018-05-08 at 19:09 -0600, Jens Axboe wrote:
>
> Alright, I managed to reproduce it. What I think is happening is that
> BFQ is limiting the inflight case to something less than the wake
> batch for sbitmap, which can lead to stalls. I don't have time to test
> this tonight, but perhaps you can give it a go when you are back at it.
> If not, I'll try tomorrow morning.
>
> If this is the issue, I can turn it into a real patch. This is just to
> confirm that the issue goes away with the below.
Confirmed. Impressive high speed bug stomping.
> diff --git a/lib/sbitmap.c b/lib/sbitmap.c
> index e6a9c06ec70c..94ced15b6428 100644
> --- a/lib/sbitmap.c
> +++ b/lib/sbitmap.c
> @@ -272,6 +272,7 @@ EXPORT_SYMBOL_GPL(sbitmap_bitmap_show);
>
> static unsigned int sbq_calc_wake_batch(unsigned int depth)
> {
> +#if 0
> unsigned int wake_batch;
>
> /*
> @@ -284,6 +285,9 @@ static unsigned int sbq_calc_wake_batch(unsigned int depth)
> wake_batch = max(1U, depth / SBQ_WAIT_QUEUES);
>
> return wake_batch;
> +#else
> + return 1;
> +#endif
> }
>
> int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
>
next prev parent reply other threads:[~2018-05-09 4:11 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-07 14:03 bug in tag handling in blk-mq? Paolo Valente
2018-05-07 16:39 ` Jens Axboe
2018-05-07 18:02 ` Paolo Valente
2018-05-08 4:51 ` Mike Galbraith
2018-05-08 8:37 ` Mike Galbraith
2018-05-08 14:55 ` Jens Axboe
2018-05-08 16:42 ` Mike Galbraith
2018-05-08 20:37 ` Jens Axboe
2018-05-08 21:19 ` Jens Axboe
2018-05-09 1:09 ` Jens Axboe
2018-05-09 4:11 ` Mike Galbraith [this message]
2018-05-09 5:06 ` Paolo Valente
2018-05-09 15:18 ` Jens Axboe
2018-05-09 16:57 ` Mike Galbraith
2018-05-09 17:01 ` Jens Axboe
2018-05-09 18:31 ` Mike Galbraith
2018-05-09 19:50 ` Jens Axboe
2018-05-10 4:38 ` Mike Galbraith
2018-05-09 5:09 ` Mike Galbraith
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