linux-kernel - Re: epoll_wait inaccurate timeout

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 12 Dec 2016 11:34:01 +0000
From:   Eric Wong <e@...24.org>
To:     Dmitry Banschikov <me@...que.spb.ru>
Cc:     linux-kernel@...r.kernel.org, John Stultz <john.stultz@...aro.org>,
        Deepa Dinamani <deepa.kernel@...il.com>
Subject: Re: epoll_wait inaccurate timeout

+Cc folks who may know about timer stuff on epoll.

Dmitry Banschikov <me@...que.spb.ru> wrote:
> Hi!
> 
> I have a problem caused by inaccurate timeouts in epoll_wait(2).
> Here are some parts of strace -tt output:

Which kernel version are you using?

> 22578 09:33:46.959791 epoll_wait(5,  <unfinished ...>
> 22578 09:33:50.010794 <... epoll_wait resumed> [], 128, 1498) = 0
> ...
> 22034 09:35:07.686896 epoll_wait(5,  <unfinished ...>
> 22034 09:35:09.482526 <... epoll_wait resumed> [{EPOLLIN,
> {u32=151458248, u64=151458248}}], 128, 362) = 1
> ...
> 22036 09:35:41.433241 epoll_wait(5,  <unfinished ...>
> 22036 09:35:43.176881 <... epoll_wait resumed> [], 128, 97) = 0
> 
> In each example epoll_wait is blocked for too longer then asked in timeout.
> 
> Is it normal?

I don't think so, unless you have a huge /proc/<pid>/timerslack_ns
set.  But I mainly use -1 or 0 as the timeout value.

> Please CC me.

That's standard procedure, here :)