linux-kernel - Re: [PATCH 2/2] block: remove the ioprio field from struct request

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Message-ID: <20241125073658.GA15834@lst.de>
Date: Mon, 25 Nov 2024 08:36:58 +0100
From: Christoph Hellwig <hch@....de>
To: Sam Protsenko <semen.protsenko@...aro.org>
Cc: Christoph Hellwig <hch@....de>, axboe@...nel.dk,
	linux-block@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] block: remove the ioprio field from struct request

On Fri, Nov 22, 2024 at 03:55:23PM -0600, Sam Protsenko wrote:
> It's an Exynos based board with eMMC, so it uses DW MMC driver, with
> Exynos glue layer on top of it, so:
> 
>     drivers/mmc/host/dw_mmc.c
>     drivers/mmc/host/dw_mmc-exynos.c
> 
> I'm using the regular ARM64 defconfig. Nothing fancy about this setup
> neither, the device tree with eMMC definition (mmc_0) is here:
> 
>     arch/arm64/boot/dts/exynos/exynos850-e850-96.dts

Thanks.  eMMC itself never looks at the ioprio field.

> FWIW, I was able to narrow down the issue to dd_insert_request()
> function. With this hack the freeze is gone:

Sounds like it isn't the driver that matters here, but the scheduler.

> 
> 8<-------------------------------------------------------------------->8
> diff --git a/block/mq-deadline.c b/block/mq-deadline.c
> index acdc28756d9d..83d272b66e71 100644
> --- a/block/mq-deadline.c
> +++ b/block/mq-deadline.c
> @@ -676,7 +676,7 @@ static void dd_insert_request(struct blk_mq_hw_ctx
> *hctx, struct request *rq,
>         struct request_queue *q = hctx->queue;
>         struct deadline_data *dd = q->elevator->elevator_data;
>         const enum dd_data_dir data_dir = rq_data_dir(rq);
> -       u16 ioprio = req_get_ioprio(rq);
> +       u16 ioprio = 0; /* the same as old req->ioprio */
>         u8 ioprio_class = IOPRIO_PRIO_CLASS(ioprio);
>         struct dd_per_prio *per_prio;
>         enum dd_prio prio;
> 8<-------------------------------------------------------------------->8
> 
> Does it tell you anything about where the possible issue can be?

Can you dump the ioprities you see here with and without the reverted
patch?