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SubjectRe: [PATCH] block,bfq: Skip tracing hooks if possible
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> Il giorno 1 nov 2019, alle ore 14:11, Dmitry Monakhov <dmonakhov@gmail.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@linaro.org>

> Signed-off-by: Dmitry Monakhov <dmonakhov@gmail.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
>

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