On Thu, Aug 03, 2017 at 02:01:55PM -0600, Jens Axboe wrote: > We don't have to inc/dec some counter, since we can just > iterate the tags. That makes inc/dec a noop, but means we > have to iterate busy tags to get an in-flight count. > > Signed-off-by: Jens Axboe <[email protected]> > --- > block/blk-mq.c | 24 ++++++++++++++++++++++++ > block/blk-mq.h | 2 ++ > block/genhd.c | 29 +++++++++++++++++++++++++++++ > include/linux/genhd.h | 25 +++---------------------- > 4 files changed, 58 insertions(+), 22 deletions(-) > > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 05dfa3f270ae..37035891e120 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -86,6 +86,30 @@ static void blk_mq_hctx_clear_pending(struct blk_mq_hw_ctx > *hctx, > sbitmap_clear_bit(&hctx->ctx_map, ctx->index_hw); > } > > +struct mq_inflight { > + struct hd_struct *part; > + unsigned int inflight; > +}; > + > +static void blk_mq_check_inflight(struct blk_mq_hw_ctx *hctx, > + struct request *rq, void *priv, > + bool reserved) > +{ > + struct mq_inflight *mi = priv; > + > + if (rq->part == mi->part) > + mi->inflight++; > +} > + > +unsigned int blk_mq_in_flight(struct request_queue *q, > + struct hd_struct *part) > +{ > + struct mq_inflight mi = { .part = part, .inflight = 0 }; > + > + blk_mq_queue_tag_busy_iter(q, blk_mq_check_inflight, &mi); > + return mi.inflight; > +}
IMO it might not be as efficient as per-cpu variable. For example, NVMe on one 128-core system, if we use percpu variable, it is enough to read 128 local variable from each CPU for accounting one in_flight. But in this way of blk_mq_in_flight(), we need to do 128 sbitmap search, and one sbitmap search need to read at least 16 words of 'unsigned long', and total 128*16 read. So maybe we need to compare the two approaches first. Thanks, Ming
