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From: Mike Galbraith <efault@gmx.de>
To: Paolo Valente <paolo.valente@linaro.org>
Cc: Jens Axboe <axboe@kernel.dk>,
	linux-block <linux-block@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Mark Brown <broonie@kernel.org>,
	linus.walleij@linaro.org, bfq-iosched@googlegroups.com,
	 oleksandr@natalenko.name
Subject: Re: [PATCH BUGFIX] block, bfq: postpone rq preparation to insert or merge
Date: Mon, 07 May 2018 07:56:37 +0200	[thread overview]
Message-ID: <1525672597.5064.3.camel@gmx.de> (raw)
In-Reply-To: <223CABEA-71E0-426F-A4AB-17BA8437C978@linaro.org>

On Sun, 2018-05-06 at 09:42 +0200, Paolo Valente wrote:
>=20
> diff --git a/block/bfq-mq-iosched.c b/block/bfq-mq-iosched.c
> index 118f319af7c0..6662efe29b69 100644
> --- a/block/bfq-mq-iosched.c
> +++ b/block/bfq-mq-iosched.c
> @@ -525,8 +525,13 @@ static void bfq_limit_depth(unsigned int op, struct =
blk_mq_alloc_data *data)
>         if (unlikely(bfqd->sb_shift !=3D bt->sb.shift))
>                 bfq_update_depths(bfqd, bt);
> =20
> +#if 0
>         data->shallow_depth =3D
>                 bfqd->word_depths[!!bfqd->wr_busy_queues][op_is_sync(op)]=
;
                                                            ^^^^^^^^^^^^^

Q: why doesn't the top of this function look like so?

---
 block/bfq-iosched.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -539,7 +539,7 @@ static void bfq_limit_depth(unsigned int
 	struct bfq_data *bfqd =3D data->q->elevator->elevator_data;
 	struct sbitmap_queue *bt;
=20
-	if (op_is_sync(op) && !op_is_write(op))
+	if (!op_is_write(op))
 		return;
=20
 	if (data->flags & BLK_MQ_REQ_RESERVED) {

It looks a bit odd that these elements exist...

+ =A0=A0=A0=A0=A0=A0/*
+ =A0=A0=A0=A0=A0=A0=A0* no more than 75% of tags for sync writes (25% extr=
a tags
+ =A0=A0=A0=A0=A0=A0=A0* w.r.t. async I/O, to prevent async I/O from starvi=
ng sync
+ =A0=A0=A0=A0=A0=A0=A0* writes)
+ =A0=A0=A0=A0=A0=A0=A0*/
+ =A0=A0=A0=A0=A0=A0bfqd->word_depths[0][1] =3D max(((1U<<bfqd->sb_shift) *=
 3)>>2, 1U);

+ =A0=A0=A0=A0=A0=A0/* no more than ~37% of tags for sync writes (~20% extr=
a tags) */
+ =A0=A0=A0=A0=A0=A0bfqd->word_depths[1][1] =3D max(((1U<<bfqd->sb_shift) *=
 6)>>4, 1U);

...yet we index via and log a guaranteed zero.

	-Mike

  parent reply	other threads:[~2018-05-07  5:56 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-04 17:17 [PATCH BUGFIX] block, bfq: postpone rq preparation to insert or merge Paolo Valente
2018-05-04 19:46 ` Mike Galbraith
2018-05-05  8:19   ` Mike Galbraith
2018-05-05 10:39     ` Paolo Valente
2018-05-05 14:56       ` Mike Galbraith
2018-05-06  7:42         ` Paolo Valente
2018-05-07  2:43           ` Mike Galbraith
2018-05-07  3:23             ` Mike Galbraith
2018-05-07  9:32               ` Paolo Valente
2018-05-07  5:56           ` Mike Galbraith [this message]
2018-05-07  9:27             ` Paolo Valente
2018-05-07 10:01               ` Mike Galbraith
2018-05-07 18:03                 ` Paolo Valente
2018-05-06  7:33 ` Oleksandr Natalenko
2018-05-10 16:14 ` Bart Van Assche
2018-05-14 17:16   ` Paolo Valente
2018-05-14 17:31     ` Jens Axboe
2018-05-14 17:37       ` Paolo Valente

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