From 3030fd4cb783377eca0e2a3eee63724a5c66ee15 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Tue, 25 Feb 2020 08:47:30 -0700 Subject: [PATCH] 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 Signed-off-by: Jens Axboe --- fs/io-wq.c | 19 ------------------- 1 file changed, 19 deletions(-) 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);