diff options
| -rw-r--r-- | hw/block/dataplane/xen-block.c | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/hw/block/dataplane/xen-block.c b/hw/block/dataplane/xen-block.c index 8e3965e171..acd23a74a8 100644 --- a/hw/block/dataplane/xen-block.c +++ b/hw/block/dataplane/xen-block.c @@ -528,10 +528,18 @@ static int xen_block_get_request(XenBlockDataPlane *dataplane, return 0; } +/* + * Threshold of in-flight requests above which we will start using + * blk_io_plug()/blk_io_unplug() to batch requests. + */ +#define IO_PLUG_THRESHOLD 1 + static void xen_block_handle_requests(XenBlockDataPlane *dataplane) { RING_IDX rc, rp; XenBlockRequest *request; + int inflight_atstart = dataplane->requests_inflight; + int batched = 0; dataplane->more_work = 0; @@ -540,6 +548,18 @@ static void xen_block_handle_requests(XenBlockDataPlane *dataplane) xen_rmb(); /* Ensure we see queued requests up to 'rp'. */ xen_block_send_response_all(dataplane); + /* + * If there was more than IO_PLUG_THRESHOLD requests in flight + * when we got here, this is an indication that there the bottleneck + * is below us, so it's worth beginning to batch up I/O requests + * rather than submitting them immediately. The maximum number + * of requests we're willing to batch is the number already in + * flight, so it can grow up to max_requests when the bottleneck + * is below us. + */ + if (inflight_atstart > IO_PLUG_THRESHOLD) { + blk_io_plug(dataplane->blk); + } while (rc != rp) { /* pull request from ring */ if (RING_REQUEST_CONS_OVERFLOW(&dataplane->rings.common, rc)) { @@ -585,7 +605,22 @@ static void xen_block_handle_requests(XenBlockDataPlane *dataplane) continue; } + if (inflight_atstart > IO_PLUG_THRESHOLD && + batched >= inflight_atstart) { + blk_io_unplug(dataplane->blk); + } xen_block_do_aio(request); + if (inflight_atstart > IO_PLUG_THRESHOLD) { + if (batched >= inflight_atstart) { + blk_io_plug(dataplane->blk); + batched = 0; + } else { + batched++; + } + } + } + if (inflight_atstart > IO_PLUG_THRESHOLD) { + blk_io_unplug(dataplane->blk); } if (dataplane->more_work && |