linux-kernel - Re: [PATCH] block: Make CFQ default to IOPS mode on SSDs

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Date:	Tue, 09 Jun 2015 12:18:32 +0200
From:	Romain Francoise <romain@...bokech.com>
To:	Tahsin Erdogan <tahsin@...gle.com>
Cc:	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block: Make CFQ default to IOPS mode on SSDs

Hi,

On Tue, May 19, 2015 at 01:55:21PM -0700, Tahsin Erdogan wrote:
> --- a/block/cfq-iosched.c
> +++ b/block/cfq-iosched.c
> @@ -4460,7 +4460,7 @@ static int cfq_init_queue(struct request_queue *q, struct elevator_type *e)
>  	cfqd->cfq_slice[1] = cfq_slice_sync;
>  	cfqd->cfq_target_latency = cfq_target_latency;
>  	cfqd->cfq_slice_async_rq = cfq_slice_async_rq;
> -	cfqd->cfq_slice_idle = cfq_slice_idle;
> +	cfqd->cfq_slice_idle = blk_queue_nonrot(q) ? 0 : cfq_slice_idle;
>  	cfqd->cfq_group_idle = cfq_group_idle;
>  	cfqd->cfq_latency = 1;
>  	cfqd->hw_tag = -1;

Did you test this patch with regular AHCI SSD devices? Applying it on
top of v4.1-rc7 makes no difference, slice_idle is still initialized to
8 in my setup, while rotational is 0.

Isn't the elevator initialized long before the non-rotational flag is
actually set on the device (which probably happens after it's probed on
the scsi bus)?
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