linux-kernel - Re: [RESEND PATCH 2/3] epoll: Add implementation for epoll

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Message-ID: <CAKgNAkiKz1pdt_uYpFDsCNLPr6UBJHZs72o3iAh57+7uG1uksQ@mail.gmail.com>
Date:	Thu, 8 Jan 2015 12:48:27 +0100
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Fam Zheng <famz@...hat.com>, lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Miklos Szeredi <mszeredi@...e.cz>,
	Juri Lelli <juri.lelli@...il.com>, Zach Brown <zab@...bo.net>,
	David Drysdale <drysdale@...gle.com>,
	Kees Cook <keescook@...omium.org>,
	Alexei Starovoitov <ast@...mgrid.com>,
	David Herrmann <dh.herrmann@...il.com>,
	Dario Faggioli <raistlin@...ux.it>,
	"Theodore Ts'o" <tytso@....edu>,
	Peter Zijlstra <peterz@...radead.org>,
	Vivek Goyal <vgoyal@...hat.com>,
	Mike Frysinger <vapier@...too.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Oleg Nesterov <oleg@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Fabian Frederick <fabf@...net.be>,
	Josh Triplett <josh@...htriplett.org>,
	"David S. Miller" <davem@...emloft.net>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	Stefan Hajnoczi <stefanha@...hat.com>
Subject: Re: [RESEND PATCH 2/3] epoll: Add implementation for epoll_pwait1

On 8 January 2015 at 12:10, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
>
> On 08/01/2015 10:16, Fam Zheng wrote:
>> Unlike ppoll(2), which accepts a timespec argument "timeout_ts" to
>> specify the timeout, epoll_wait(2) and epoll_pwait(2) expect a
>> microsecond timeout in int type.
>>
>> This is an obstacle for applications in switching from ppoll to epoll,
>> if they want nanosecond resolution in their event loops.
>>
>> Therefore, adding this variation of epoll wait interface, giving user an
>> option with *both* advantages, is a reasonable move: there could be
>> constantly scalable performance polling many fds, while having a
>> nanosecond timeout precision (assuming it has properly set up timer
>> slack with prctl(2)).
>>
>> Signed-off-by: Fam Zheng <famz@...hat.com>
>> ---
>>  fs/eventpoll.c           | 24 ++++++++++++++++++++++++
>>  include/linux/syscalls.h |  4 ++++
>>  kernel/sys_ni.c          |  3 +++
>>  3 files changed, 31 insertions(+)
>
> As mentioned by Miklos in the non-resent version, please add a flags
> argument.  Invalid flags should return -EINVAL.
>
> In fact, we could already use the flags argument to specify an absolute
> timeout, which is a nice thing to have for QEMU too.

Nice! It looks like we found this iteration of "failure to include a
flags argument is a mistake" already!

Cheers,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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