Re: [PATCH V2 2/3] blk-mq: only attempt to merge bio if there is rq in sw queue

Christoph Hellwig
2018-06-29T08:35:02Z

On Fri, Jun 29, 2018 at 04:12:51PM +0800, Ming Lei wrote:
> Only attempt to merge bio iff the ctx->rq_list isn't empty, because:
>
> 1) for high-performance SSD, most of times dispatch may succeed, then
> there may be nothing left in ctx->rq_list, so don't try to merge over
> sw queue if it is empty, then we can save one acquiring of ctx->lock
>
> 2) we can't expect good merge performance on per-cpu sw queue, and missing
> one merge on sw queue won't be a big deal since tasks can be scheduled from
> one CPU to another.

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>