linux-kernel - Re: unpredictability in scheduler test results -- still present

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]

Message-ID: <20080927200433.GC28937@elte.hu>
Date:	Sat, 27 Sep 2008 22:04:33 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Chris Friesen <cfriesen@...tel.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: unpredictability in scheduler test results -- still present


* Chris Friesen <cfriesen@...tel.com> wrote:

> Chris Friesen wrote:
>
>> This behaviour (that load balancing is messed up) is now almost  
>> continuous with both current tip/master and current Linus git.  On the  
>> first test after booting, it seems to work okay (although there are  
>> still issues with fairness).  On every subsequent test, fairness is 
>> good but it only uses one of the two cpus.
>>
>> Also, building a kernel with "-j10" results in one cpu being mostly 
>> idle while the other one is 100% busy. It used to be both 100% busy--if 
>> I get time today I may try bisecting it.
>
> It turns out that disabling CONFIG_DYNAMIC_FTRACE makes the load 
> balancing problem go away and causes all cpus to be used.
>
> With this option enabled, the problem seems to be present as far back 
> as 2.6.27-rc2.  (2.6.27-rc1 doesn't compile on my machine, and 2.6.26 
> doesn't have ftrace).
>
> I have no idea why turning on dynamic ftrace would affect load 
> balancing behaviour, but it's very repeatable.  The very first test 
> run after booting works fine, and all successive runs fail to balance 
> properly.

very weird. Would be very nice to figure it out.

and in tip/master we dont have the 'ftraced' kernel-patching kernel 
thread anymore, so ftrace should be passive by all means.

OTOH, what does 'truning on dftrace' exactly mean? Just enabling it in 
the .config, or also activating it via /debug/tracing/current_tracer?

	Ingo
--
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/