Re: Performance degradation in commit ac1d794

From: Andres Freund <andres(at)anarazel(dot)de>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Васильев Дмитрий <d(dot)vasilyev(at)postgrespro(dot)ru>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Performance degradation in commit ac1d794
Date: 2016-03-18 17:53:36
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On 2016-03-18 05:56:41 -0400, Robert Haas wrote:
> >> 0 at the top of the loop and skip it forthwith if so.
> >
> > You mean in WaitEventSetWait()? There's
> > else if (rc == 0)
> > {
> > break;
> > }
> > which is the timeout case. There should never be any other case of
> > returning 0 elements?
> No, I meant if (cur_event->events == 0) continue;

I'm not following. Why would there be an event without an empty event
mask? Ok, you can disable all notifications for a socket using
ModifyWaitEvent(), but that's not particularly common, right? At least
for epoll, it'd not play a role anyway, since epoll_wait() will actually
return pointers to the elements we're waiting on; for windows we get the
offset in ->handles. I guess we could do so in the select/poll case,
but adding another if for something infrequent doesn't strike me as a
great benefit.

- Andres

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