linux-kernel - Re: [PATCH] rfc: threaded epoll

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:	Sat, 5 May 2007 12:00:29 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Davi Arnaut <davi@...ent.com.br>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rfc: threaded epoll_wait thundering herd

On Fri, 4 May 2007, Davi Arnaut wrote:

> Hi,
> 
> If multiple threads are parked on epoll_wait (on a single epoll fd) and
> events become available, epoll performs a wake up of all threads of the
> poll wait list, causing a thundering herd of processes trying to grab
> the eventpoll lock.
> 
> This patch addresses this by using exclusive waiters (wake one). Once
> the exclusive thread finishes transferring it's events, a new thread
> is woken if there are more events available.
> 
> Makes sense?

Theorically, make sense. I said theorically because all the use 
epoll_wait MT use cases I've heard of, use a single thread that does the 
epoll_wait, and then dispatch to worker threads. So thundering herd is not 
in the picture. OTOH, it does not hurt either.
But, that code is completely changed with the new single-pass epoll delivery 
code that is in -mm. So, I'd either wait for that code to go in, or I 
(or you, if you like) can make a patch against -mm.

- Davide

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/