On 9/6/24 12:14, ZhangHui wrote:
> From: zhanghui <zhanghui31@xxxxxxxxxx>
>
> Currently, for a controller that supports multiple queues, like UFS4.0,
> the mq_ops->complete is executed in the interrupt top-half. Therefore,
> the file system's end io is executed during the request completion process,
> such as f2fs_write_end_io on smartphone.
>
> However, we found that the execution time of the file system end io
> is strongly related to the size of the bio and the processing speed
> of the CPU. Because the file system's end io will traverse every page
> in bio, this is a very time-consuming operation.
>
> We measured that the 80M bio write operation on the little CPU will
> cause the execution time of the top-half to be greater than 100ms,
> which will undoubtedly affect interrupt response latency.
>
> Let's fixed this issue by moved non sync request completion flow to
> softirq, and keep the sync request completion in the top-half.
Typos/grammar:
Let's fix this issue by moving non sync requests completion to softirq context,
and keeping sync requests completion in the irq top-half context.
>
> Signed-off-by: zhanghui <zhanghui31@xxxxxxxxxx>
> ---
> Changes in v4:
> - fix commit log from "scheduling efficiency" to "interrupt response latency"
>
> Changes in v3:
> - modify op_is_sync to rq_is_sync
>
> Changes in v2:
> - fix build warning
> ---
> block/blk-mq.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index e3c3c0c21b55..06b232edff11 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1193,6 +1193,8 @@ static void blk_mq_raise_softirq(struct request *rq)
>
> bool blk_mq_complete_request_remote(struct request *rq)
> {
> + const bool is_sync = rq_is_sync(rq);
> +
> WRITE_ONCE(rq->state, MQ_RQ_COMPLETE);
>
> /*
> @@ -1210,7 +1212,7 @@ bool blk_mq_complete_request_remote(struct request *rq)
> return true;
> }
>
> - if (rq->q->nr_hw_queues == 1) {
> + if ((rq->q->nr_hw_queues == 1) || !is_sync) {
I do not see the point of the is_sync variable, and you do not need the inner
parenthesis either. Why not:
if (rq->q->nr_hw_queues == 1 || !rq_is_sync(rq)) {
And a comment before the "if" explaining why soft-irq is raised for non-sync
requests would be nice too.
> blk_mq_raise_softirq(rq);
> return true;
> }
--
Damien Le Moal
Western Digital Research
