From mboxrd@z Thu Jan  1 00:00:00 1970
From: Fam Zheng <famz-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH RFC 0/6] epoll: Introduce new syscall "epoll_mod_wait"
Date: Tue, 20 Jan 2015 18:53:38 +0800
Message-ID: <20150120105338.GA4040@ad.nay.redhat.com>
References: <1421747878-30744-1-git-send-email-famz@redhat.com>
 <874mrl3fh9.fsf@rasmusvillemoes.dk>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>,
	Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	"H. Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>, x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org,
	Alexander Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>,
	Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
	Kees Cook <keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>,
	Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>,
	David Herrmann <dh.herrmann-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	Alexei Starovoitov <ast-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>,
	Miklos Szeredi <mszeredi-AlSwsSmVLrQ@public.gmane.org>,
	David Drysdale <drysdale-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
	Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	"David S. Miller" <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>,
	Vivek Goyal <vgoyal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Mike Frysinger <vapier-aBrp7R+bbdUdnm+yROfE0A@public.gmane.org>,
	"Theodore Ts'o" <tytso-3s7WtUTddSA@public.gmane.org>,
	Heiko Carstens <heiko.carstens-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>,
	Rashika Kheria <rashika.kheria-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	Hugh Dickins <hughd-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
	Mathieu Desnoyers <mathieu.desnoyers-vg+e7yoeK/dWk0Htik3J/w@public.gmane.org>,
	Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
	linux-fsdevel-u79uwXL29TbrhsbdSgBK9A@public.gmane.org
To: Rasmus Villemoes <linux-qQsb+v5E8BnlAoU/VqSP6n9LOBIZ5rWg@public.gmane.org>
Return-path: <linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Content-Disposition: inline
In-Reply-To: <874mrl3fh9.fsf-qQsb+v5E8BnlAoU/VqSP6n9LOBIZ5rWg@public.gmane.org>
Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
List-Id: linux-fsdevel.vger.kernel.org

On Tue, 01/20 11:37, Rasmus Villemoes wrote:
> On Tue, Jan 20 2015, Fam Zheng <famz-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
> 
> > DESCRIPTION
> >
> >        The epoll_mod_wait() system call can be seen as an enhanced combination
> >        of several epoll_ctl(2) calls, which are followed by an epoll_pwait(2)
> >        call. It is superior in two cases:
> >        
> >        1) When epoll_ctl(2) are followed by epoll_wait(2), using epoll_mod_wait
> >        will save context switches between user mode and kernel mode;
> >        
> >        2) When you need higher precision than microsecond for wait timeout.
> 
> You probably want to say millisecond.

Yes, you see that I just can't make this right. :)

> 
> >            struct epoll_mod_cmd {
> [...]
> >            };
> 
> 
> >            struct epoll_wait_spec {
> [...]
> >            } EPOLL_PACKED;
> 
> Either both or none of these should mention that EPOLL_PACKED is in fact
> part of the actual definition. The changelog for 3/6 sorta mentions
> that it's not really needed for epoll_mod_cmd. Why is it necessary for
> either struct?

Yeah. it's probably not really necessary.

> 
> > RETURN VALUE
> >
> >        When successful, epoll_mod_wait() returns the number of file
> >        descriptors ready for the requested I/O, or zero if no file descriptor
> >        became ready during the requested timeout milliseconds.
> 
> And here, it doesn't make sense to mention a unit, since the new timeout
> is given using struct timespec (this was the whole point, right?).

Right!

Thanks,
Fam