linux-kernel - Re: [RFC PATCH 0/3] epoll: read(),write(),ioctl() interface

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Message-ID: <CALCETrX1GE0w8nXMxRHmgqRS8_hKwZ8dq+T1c4DPip8Jh+-8Dw@mail.gmail.com>
Date:	Mon, 3 Feb 2014 14:06:04 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Eric Wong <normalperson@...t.net>
Cc:	Nathaniel Yazdani <n1ght.4nd.d4y@...il.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/3] epoll: read(),write(),ioctl() interface

On Mon, Feb 3, 2014 at 1:51 PM, Eric Wong <normalperson@...t.net> wrote:
> Andy Lutomirski <luto@...capital.net> wrote:
>> >> On 02/02/2014 06:17 PM, Nathaniel Yazdani wrote:
>> > So are you saying that those features you mentioned are specifically sought
>> > after for the kernel? If so I'd like to take a crack at some of them,
>> > may as well
>> > get some use out of my new knowledge of epoll internals :)
>>
>> If by "sought after", you mean "is there at least one epoll user who
>> wants them", then yes :)
>>
>> I think that EPOLLET and EPOLLONESHOT are giant hacks, and that what
>> everyone really wants is the ability to very efficiently toggle events
>> on and off.  The ability to do it simultaneously and inexpensively
>> with epoll_wait would make it happen.
>
> Everybody using single-threaded epoll, you mean?  I suppose there's
> quite a few of those.
>
> I've pondered an epoll_xchg syscall which would behave like *BSD kevent
> to satisfy single-threaded users, but never got around to it.  All my
> epoll uses are multithreaded w/ oneshot nowadays, so xchg would only
> save one syscall per thread.

Even for multithreaded, the ability to rearm EPOLLONESHOT entries
without extra syscalls would probably be useful.

--Andy
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