On Mon, Nov 04, 2019 at 01:14:03PM -0500, Kent Overstreet wrote: > On Sat, Nov 02, 2019 at 03:29:11PM +0800, Ming Lei wrote: > > __blk_queue_split() may be a bit heavy for small block size(such as > > 512B, or 4KB) IO, so introduce one flag to decide if this bio includes > > multiple page. And only consider to try splitting this bio in case > > that the multiple page flag is set. > > So, back in the day I had an alternative approach in mind: get rid of > blk_queue_split entirely, by pushing splitting down to the request layer - when > we map the bio/request to sgl, just have it map as much as will fit in the sgl > and if it doesn't entirely fit bump bi_remaining and leave it on the request > queue. Many drivers don't need sgl via blk_rq_map_sg(), but still need to split bio. > > This would mean there'd be no need for counting segments at all, and would cut a > fair amount of code out of the io path. No counting segments involved in this small block size case, the handling in blk_bio_segment_split() should be simple enough, still not understand why IOPS drop is observable. Thanks, Ming
