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From: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: David Laight <David.Laight@aculab.com>,
	Arnd Bergmann <arnd@kernel.org>,
	Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Andrew Morton <akpm@linux-foundation.org>,
	Soheil Hassas Yeganeh <soheil.kdev@gmail.com>,
	Arnd Bergmann <arnd@arndb.de>, Shuo Chen <shuochen@google.com>,
	linux-man <linux-man@vger.kernel.org>,
	Willem de Bruijn <willemb@google.com>
Subject: Re: [PATCH v3 1/2] epoll: add nsec timeout support with epoll_pwait2
Date: Thu, 19 Nov 2020 10:37:02 -0500	[thread overview]
Message-ID: <CAF=yD-+D8E9ksXrWe8ezd-B9pdu7PhMwGjG4gCBvuABRahrsAw@mail.gmail.com> (raw)
In-Reply-To: <20201119143131.GG29991@casper.infradead.org>

On Thu, Nov 19, 2020 at 9:31 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Thu, Nov 19, 2020 at 09:19:35AM -0500, Willem de Bruijn wrote:
> > But for epoll, this is inefficient: in ep_set_mstimeout it calls
> > ktime_get_ts64 to convert timeout to an offset from current time, only
> > to pass it to select_estimate_accuracy to then perform another
> > ktime_get_ts64 and subtract this to get back to (approx.) the original
> > timeout.
> >
> > How about a separate patch that adds epoll_estimate_accuracy with
> > the same rules (wrt rt_task, current->timer_slack, nice and upper bound)
> > but taking an s64 timeout.
> >
> > One variation, since it is approximate, I suppose we could even replace
> > division by a right shift?
> >
> > After that, using s64 everywhere is indeed much simpler. And with that
> > I will revise the new epoll_pwait2 interface to take a long long
> > instead of struct timespec.
>
> I think the userspace interface should take a struct timespec
> for consistency with ppoll and pselect. And epoll should use
> poll_select_set_timeout() to convert the relative timeout to an absolute
> endtime.  Make epoll more consistent with select/poll, not less ...

Okay. The absolute time is also needed for schedule_hrtimeout_range,
so it could not be entirely avoided, anyway.

  reply	other threads:[~2020-11-19 15:38 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-18 14:46 [PATCH v3 0/2] add epoll_pwait2 syscall Willem de Bruijn
2020-11-18 14:46 ` [PATCH v3 1/2] epoll: add nsec timeout support with epoll_pwait2 Willem de Bruijn
2020-11-18 15:00   ` Matthew Wilcox
2020-11-18 15:10     ` Willem de Bruijn
2020-11-18 15:37       ` Arnd Bergmann
2020-11-18 15:59         ` David Laight
2020-11-19 14:19           ` Willem de Bruijn
2020-11-19 14:31             ` Matthew Wilcox
2020-11-19 15:37               ` Willem de Bruijn [this message]
2020-11-19 15:45               ` Arnd Bergmann
2020-11-19 20:13                 ` Willem de Bruijn
2020-11-20  8:13                   ` Arnd Bergmann
2020-11-20 16:01                     ` Willem de Bruijn
2020-11-20 19:23                       ` Arnd Bergmann
2020-11-20 22:28                         ` Willem de Bruijn
2020-11-21  9:27                           ` Arnd Bergmann
2020-12-10 17:33                             ` Willem de Bruijn
2020-12-10 20:34                               ` Arnd Bergmann
2020-12-10 22:59                                 ` Willem de Bruijn
2021-01-11 20:06                                   ` Willem de Bruijn
2020-11-18 16:21   ` Willem de Bruijn
2020-11-18 16:50     ` Arnd Bergmann
2020-11-19  3:22       ` Willem de Bruijn
2020-11-18 14:46 ` [PATCH manpages RFC] epoll_wait.2: add epoll_pwait2 Willem de Bruijn
2020-11-18 14:46 ` [PATCH v3 2/2] selftests/filesystems: expand epoll with epoll_pwait2 Willem de Bruijn

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