Andres reports that buffered IO seems to suck up more cycles than we
would like, and he narrowed it down to the fact that the io-wq workers
will briefly spin for more work on completion of a work item. This was
a win on the networking side, but apparently some other cases take a
hit because of it. Remove the optimization to avoid burning more CPU
than we have to for disk IO.
Reported-by: Andres Freund <andres@xxxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
diff --git a/fs/io-wq.c b/fs/io-wq.c
index 0a5ab1a8f69a..bf8ed1b0b90a 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -535,42 +535,23 @@ static void io_worker_handle_work(struct io_worker *worker)
} while (1);
}
-static inline void io_worker_spin_for_work(struct io_wqe *wqe)
-{
- int i = 0;
-
- while (++i < 1000) {
- if (io_wqe_run_queue(wqe))
- break;
- if (need_resched())
- break;
- cpu_relax();
- }
-}
-
static int io_wqe_worker(void *data)
{
struct io_worker *worker = data;
struct io_wqe *wqe = worker->wqe;
struct io_wq *wq = wqe->wq;
- bool did_work;
io_worker_start(wqe, worker);
- did_work = false;
while (!test_bit(IO_WQ_BIT_EXIT, &wq->state)) {
set_current_state(TASK_INTERRUPTIBLE);
loop:
- if (did_work)
- io_worker_spin_for_work(wqe);
spin_lock_irq(&wqe->lock);
if (io_wqe_run_queue(wqe)) {
__set_current_state(TASK_RUNNING);
io_worker_handle_work(worker);
- did_work = true;
goto loop;
}
- did_work = false;
/* drops the lock on success, retry */
if (__io_worker_idle(wqe, worker)) {
__release(&wqe->lock);
--
Jens Axboe
