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Message-ID: <54AE65BB.1020707@redhat.com>
Date: Thu, 08 Jan 2015 12:10:51 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Fam Zheng <famz@...hat.com>, linux-kernel@...r.kernel.org
CC: Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, 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-api@...r.kernel.org,
Stefan Hajnoczi <stefanha@...hat.com>
Subject: Re: [RESEND PATCH 2/3] epoll: Add implementation for epoll_pwait1
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.
Paolo
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