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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>
This commit is contained in:
Jens Axboe 2020-02-25 08:47:30 -07:00
parent bdcd3eab2a
commit 3030fd4cb7
1 changed files with 0 additions and 19 deletions
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19
fs/io-wq.c
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@ -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);