On 4/20/22 08:16, Stefan Hajnoczi wrote: > On Tue, Apr 19, 2022 at 09:10:52PM -0700, Chaitanya Kulkarni wrote: >> We can avoid a function call virtblk_map_data() in the fast path if >> block layer request has no physical segments by moving the call >> blk_rq_nr_phys_segments() from virtblk_map_data() to virtio_queue_rq(). >> >> Signed-off-by: Chaitanya Kulkarni <kch@xxxxxxxxxx> >> --- >> drivers/block/virtio_blk.c | 15 +++++++-------- >> 1 file changed, 7 insertions(+), 8 deletions(-) > > virtblk_map_data() is a static function that is not called by anything > else in virtio_blk.c. The disassembly on my x86_64 machine shows it has > been inlined into virtio_queue_rq(). The compiler has already done what > this patch is trying to do (and more). > > Can you share performance data or some more background on why this > code change is necessary? > > I don't have performance numbers, but when reading the code it takes to a function call especially in the fast path where read/write requests has phys segments and those are probably most frequent requests... I'll drop it from V2, if I find performance numbers then I'll repost is with the quantitative data ... -ck
