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Date: Thu, 08 Jan 2015 12:10:51 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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To: Fam Zheng <famz@redhat.com>, linux-kernel@vger.kernel.org
CC: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        Alexander Viro <viro@zeniv.linux.org.uk>,
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        Fabian Frederick <fabf@skynet.be>,
        Josh Triplett <josh@joshtriplett.org>,
        "David S. Miller" <davem@davemloft.net>, linux-fsdevel@vger.kernel.org,
        linux-api@vger.kernel.org, Stefan Hajnoczi <stefanha@redhat.com>
Subject: Re: [RESEND PATCH 2/3] epoll: Add implementation for epoll_pwait1
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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@redhat.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