linux-kernel - Re: [PATCH] block,bfq: Skip tracing hooks if possible

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Date:   Fri, 15 Nov 2019 07:47:43 +0100
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Dmitry Monakhov <dmonakhov@...il.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>, axboe@...nel.dk
Subject: Re: [PATCH] block,bfq: Skip tracing hooks if possible



> Il giorno 1 nov 2019, alle ore 14:11, Dmitry Monakhov <dmonakhov@...il.com> ha scritto:
> 
> In most cases blk_tracing is not active, but  bfq_log_bfqq macro
> generate pid_str unconditionally, which result in significant overhead.
> 
> ## Test
> modprobe null_blk
> echo bfq > /sys/block/nullb0/queue/scheduler
> fio --name=t --ioengine=libaio --direct=1 --filename=/dev/nullb0 \
>   --runtime=30 --time_based=1 --rw=write --iodepth=128 --bs=4k
> 
> # Results
> |        | baseline | w/ patch | gain |
> | iops   | 113.19K  | 126.42K  | +11% |
> 

Thank you very much for this simple yet effective improvement.

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

> Signed-off-by: Dmitry Monakhov <dmonakhov@...il.com>
> ---
> block/bfq-iosched.h | 4 ++++
> 1 file changed, 4 insertions(+)
> 
> 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);
> 
> #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);
> 
> #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',		\
> -- 
> 2.7.4
>