Re: [PATCH RFC 5/6] epoll: Add implementation for epoll_mod_wait

[Andy Lutomirski]

On Wed, Jan 21, 2015 at 3:50 AM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
>
> On 21/01/2015 12:14, Fam Zheng wrote:
>> > My take for simplicity will be leaving epoll_ctl as-is, and my take for
>> > performance will be epoll_pwait1. And I don't really like putting my time on
>> > epoll_ctl_batch, thinking it as a ambivalent compromise in between.
>>
>> > I agree with Michael actually.  The big change is going from O(n)
>> > epoll_ctl calls to O(1), and epoll_ctl_batch achieves that just fine.
>> > Changing 2 syscalls to 1 is the icing on the cake, but we're talking of
>> > a fraction of a microsecond.
>>
>> Maybe I'm missing something, but in common cases, the set of fds for epoll_wait
>> doesn't change that radically from one iteration to another, does it?
>
> That depends on the application.

In my application, the set of fds almost never changes, but the set of
events I want changes all the time.  The main thing that changes is
whether I care about EPOLLOUT.  If I'm ready to send something, then I
want EPOLLOUT.  If I'm not ready, then I don't want EPOLLOUT.

--Andy
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