On Thu, 06 Apr 2017 03:54:19 +0200 Mike Galbraith <efa...@gmx.de> wrote:
> On Wed, 2017-04-05 at 16:42 -0700, Cong Wang wrote: > > On Tue, Apr 4, 2017 at 10:56 PM, Mike Galbraith <efa...@gmx.de> wrote: > > > On Tue, 2017-04-04 at 22:19 -0700, Cong Wang wrote: > > > > On Tue, Apr 4, 2017 at 8:55 PM, Mike Galbraith <efa...@gmx.de> wrote: > > > > > > > > That won't help, cond_resched() has the same impact upon a lone > > > > > SCHED_FIFO task as yield() does.. none. > > > > > > > > Hmm? In the comment you quote: > > > > > > > > * If you want to use yield() to wait for something, use wait_event(). > > > > * If you want to use yield() to be 'nice' for others, use > > > > cond_resched(). > > > > > > > > So if cond_resched() doesn't help, why this misleading comment? > > > > > > This is not an oh let's be nice guys thing, it's a perfect match of... > > > > > > > > > * while (!event) > > > * yield(); > > > (/copy/paste> > > > > > > ..get off the CPU until this happens thing. With nobody to yield the C > > > PU to, some_qdisc_is_busy() will remain true forever more. > > > > > > This is exactly the misleading part, a while-loop waiting for an event > > can always be a be-nice-for-others thing, because if not we can just > > spin as a spinlock. > > Ah, but the kworker _is_ spinning on a 'lock' or sorts, starving the > 'owner', ergo this polling loop fails the 'may be nice' litmus test. > No polling loop is safe without a guarantee that the polling thread > cannot block the loop breaking event. > > -Mike Why not replace yield with msleep(1) which gets rid of the inversion issues?
