linux-kernel - Re: cgroups: Assigning tasks to a cgroup slow and does not scale

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] [day] [month] [year] [list]

Date:	Sat, 04 Jun 2011 12:10:31 +0200
From:	Mike Galbraith <efault@....de>
To:	Martin Baum <pop3@...chtaucher.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: cgroups: Assigning tasks to a cgroup slow and does not scale

On Sat, 2011-06-04 at 10:23 +0200, Martin Baum wrote:
> Hello,
> 
> assigning a task to new cgroup takes an unexpected high amount of time  
> on my system - about 0.05s. Strangely it does it does not scale with  
> more processes: When I run 10 processes that do nothing but change  
> their cgroups each cgroup change takes about 0.5 seconds while CPU  
> usage remains very low. So my system maxes out at 20 cgroup changes  
> per second while cpu and disk usage remain minimal (according to top).  
> Is this expected behaviour?

Attaching a task invokes synchronize_rcu() along the way, so yup, it's
the expected behavior.

> It is a problem for me: I run a daemon that forks and calls suid for  
> each request. I want to assign each of these forks to a different  
> cgroup. However this currently kills performance going down from >100  
> req/sec to about 20 req/sec.

You can work around it via static cgroups with an agent waiting inside
each one.  Tell your agent what to do, he forks off a worker.  You can
inherit a cgroup quickly, but moving between cgroups is very expensive,
as you noticed.

(right way is eventually stop exporting rcu grace periods to userland)

	-Mike

--
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/