linux-kernel - Re: RCU related performance regression in 3.3

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:	Fri, 6 Apr 2012 11:18:03 +0200 (CEST)
From:	Pascal Chapperon <pascal.chapperon@...adoo.fr>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Josh Boyer <jwboyer@...hat.com>, linux-kernel@...r.kernel.org,
	kernel-team@...oraproject.org
Subject: Re: RCU related performance regression in 3.3

> Message du 05/04/12 16:40
> De : "Paul E. McKenney" 
> A : "Pascal CHAPPERON" 
> Copie à : "Josh Boyer" , linux-kernel@...r.kernel.org, kernel-team@...oraproject.org
> Objet : Re: RCU related performance regression in 3.3
> 
> On Thu, Apr 05, 2012 at 04:15:33PM +0200, Pascal CHAPPERON wrote:
> > Hello,
> > 
> > I didn't notice any significant slowdown while the system is up and running. 
A full kernel compilation (make -j 16) takes 14mn with both 3.2.10 and 3.3.0.
> 
> OK, so the natural approach is to disable CONFIG_RCU_FAST_NO_HZ at
> boot time. Unfortunately, you appear to need it to remain disabled
> through at least filesystem mounting, which if I understand correctly
> happens long after system_state gets set to SYSTEM_RUNNING.
> 
In fact, I need it to remain disable until all the systemd units are completed. 
Some units, such as NetworkManager can take longer time to complete with
RCU_FAST_NO_HZ enabled.
And i need it to be disabled at shutdown, as umounting cgroups, sysfs, etc.
plus old-root mounting can take one plain second for each umounting.

> If RCU has some way to find out when init is complete, I can easily
> make it so that CONFIG_RCU_FAST_NO_HZ optimizes for speed during boot
> and energy efficiency during runtime.
> 
I said that I didn't noticed significant slowdown during runtime, but my
laptop usage is basic. Some specific tasks similar to systemd may 
perhaps be impacted by this feature.
I can test a task/program that could stress RCU_FAST_NO_HZ if any ?

> One thing I could easily do would be to provide a sysfs parameter or
> some such that allows the boot process to enable energy-efficiency
> mode at runtime. I would much prefer to make this automatic, though.
> 
So the feature is disabled until you trigger a sysfs parameter, and can be
disabled before shutdown ? It would be fair, at least for hardware like my
own.

> Other thoughts?
> 
Do you think that the culprit is a buggy hardware in my laptop, or the 
number of cpu/threads ?

> Thanx, Paul
> 

Resent in plain text because rejected. Sorry, i forgot the rules.

Pascal
--
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/