We currently spin in iopoll() when requests to be iopolled are for
same file(device), while one device may have multiple hardware queues.
given an example:
hw_queue_0 | hw_queue_1
req(30us) req(10us)
If we first spin on iopolling for the hw_queue_0. the avg latency would
be (30us + 30us) / 2 = 30us. While if we do round robin, the avg
latency would be (30us + 10us) / 2 = 20us since we reap the request in
hw_queue_1 in time. So it's better to do spinning only when requests
are in same hardware queue.
Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
struct list_head iopoll_list;
struct hlist_head *cancel_hash;
unsigned cancel_hash_bits;
struct list_head iopoll_list;
struct hlist_head *cancel_hash;
unsigned cancel_hash_bits;
} ____cacheline_aligned_in_smp;
struct io_restriction restrictions;
} ____cacheline_aligned_in_smp;
struct io_restriction restrictions;
* Only spin for completions if we don't have multiple devices hanging
* off our complete list, and we're under the requested amount.
*/
* Only spin for completions if we don't have multiple devices hanging
* off our complete list, and we're under the requested amount.
*/
- spin = !ctx->poll_multi_file && *nr_events < min;
+ spin = !ctx->poll_multi_queue && *nr_events < min;
ret = 0;
list_for_each_entry_safe(req, tmp, &ctx->iopoll_list, inflight_entry) {
ret = 0;
list_for_each_entry_safe(req, tmp, &ctx->iopoll_list, inflight_entry) {
* different devices.
*/
if (list_empty(&ctx->iopoll_list)) {
* different devices.
*/
if (list_empty(&ctx->iopoll_list)) {
- ctx->poll_multi_file = false;
- } else if (!ctx->poll_multi_file) {
+ ctx->poll_multi_queue = false;
+ } else if (!ctx->poll_multi_queue) {
struct io_kiocb *list_req;
struct io_kiocb *list_req;
+ unsigned int queue_num0, queue_num1;
list_req = list_first_entry(&ctx->iopoll_list, struct io_kiocb,
inflight_entry);
list_req = list_first_entry(&ctx->iopoll_list, struct io_kiocb,
inflight_entry);
- if (list_req->file != req->file)
- ctx->poll_multi_file = true;
+
+ if (list_req->file != req->file) {
+ ctx->poll_multi_queue = true;
+ } else {
+ queue_num0 = blk_qc_t_to_queue_num(list_req->rw.kiocb.ki_cookie);
+ queue_num1 = blk_qc_t_to_queue_num(req->rw.kiocb.ki_cookie);
+ if (queue_num0 != queue_num1)
+ ctx->poll_multi_queue = true;
+ }