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Subject: Re: [PATCH] block,bfq: Skip tracing hooks if possible
From:   Paolo Valente <paolo.valente@linaro.org>
In-Reply-To: <20191101131110.18356-1-dmonakhov@gmail.com>
Date:   Fri, 15 Nov 2019 07:47:43 +0100
Cc:     linux-kernel <linux-kernel@vger.kernel.org>, axboe@kernel.dk
Content-Transfer-Encoding: quoted-printable
Message-Id: <A32330F0-ADD6-43F8-B0EE-89A0D0568867@linaro.org>
References: <20191101131110.18356-1-dmonakhov@gmail.com>
To:     Dmitry Monakhov <dmonakhov@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> Il giorno 1 nov 2019, alle ore 14:11, Dmitry Monakhov =
<dmonakhov@gmail.com> ha scritto:
>=20
> In most cases blk_tracing is not active, but  bfq_log_bfqq macro
> generate pid_str unconditionally, which result in significant =
overhead.
>=20
> ## Test
> modprobe null_blk
> echo bfq > /sys/block/nullb0/queue/scheduler
> fio --name=3Dt --ioengine=3Dlibaio --direct=3D1 --filename=3D/dev/nullb0=
 \
>   --runtime=3D30 --time_based=3D1 --rw=3Dwrite --iodepth=3D128 --bs=3D4k=

>=20
> # Results
> |        | baseline | w/ patch | gain |
> | iops   | 113.19K  | 126.42K  | +11% |
>=20

Thank you very much for this simple yet effective improvement.

Acked-by: Paolo Valente <paolo.valente@linaro.org>

> Signed-off-by: Dmitry Monakhov <dmonakhov@gmail.com>
> ---
> block/bfq-iosched.h | 4 ++++
> 1 file changed, 4 insertions(+)
>=20
> diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
> index 5d1a519..b320fe9 100644
> --- a/block/bfq-iosched.h
> +++ b/block/bfq-iosched.h
> @@ -1062,6 +1062,8 @@ struct bfq_group *bfqq_group(struct bfq_queue =
*bfqq);
>=20
> #define bfq_log_bfqq(bfqd, bfqq, fmt, args...)	do {			=
\
> 	char pid_str[MAX_PID_STR_LENGTH];	\
> +	if (likely(!blk_trace_note_message_enabled((bfqd)->queue)))	=
\
> +		break;							=
\
> 	bfq_pid_to_str((bfqq)->pid, pid_str, MAX_PID_STR_LENGTH);	=
\
> 	blk_add_cgroup_trace_msg((bfqd)->queue,				=
\
> 			bfqg_to_blkg(bfqq_group(bfqq))->blkcg,		=
\
> @@ -1078,6 +1080,8 @@ struct bfq_group *bfqq_group(struct bfq_queue =
*bfqq);
>=20
> #define bfq_log_bfqq(bfqd, bfqq, fmt, args...) do {	\
> 	char pid_str[MAX_PID_STR_LENGTH];	\
> +	if (likely(!blk_trace_note_message_enabled((bfqd)->queue)))	=
\
> +		break;							=
\
> 	bfq_pid_to_str((bfqq)->pid, pid_str, MAX_PID_STR_LENGTH);	=
\
> 	blk_add_trace_msg((bfqd)->queue, "bfq%s%c " fmt, pid_str,	=
\
> 			bfq_bfqq_sync((bfqq)) ? 'S' : 'A',		=
\
> --=20
> 2.7.4
>=20