io-wq: remove spin-for-work optimization

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@anarazel.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io-wq.c b/fs/io-wq.c
index 0a5ab1a..bf8ed1b 100644 (file)
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -535,42 +535,23 @@ next:
        } 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);