linux-kernel - Re: Idle power fix regresses ebizzy performance (was 3.12-stable backport of NUMA balancing patches)

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, 13 Jan 2014 19:24:06 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Len Brown <len.brown@...el.com>
Cc:	athorlton@....com, riel@...hat.com, chegu_vinod@...com,
	Greg KH <gregkh@...uxfoundation.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>, stable@...r.kernel.org
Subject: Re: Idle power fix regresses ebizzy performance (was 3.12-stable
 backport of NUMA balancing patches)

On Wed, Jan 08, 2014 at 01:48:58PM +0000, Mel Gorman wrote:
> Adding LKML to the list as this -stable snifftest has identified an
> upstream regression.
> 

This is a false alarm.

The test machine in question was originally installed based on a beta
version of openSUSE 13.1. It included a package by default that set default
malloc parameters that I was not aware. Normally the package is there to
catch bugs during beta testing and removed before a GA release but it's
left in place if a user does a distribution update.

With the debugging RPM installed, the free paths contended on a global
mutex in glibc.  Ebizzy had been classified as a CPU intensive and memory
free intensive benchmark (not that common) but turbostat showed that the
CPUs were over 95% of the time in C6 and mpstat verified that the CPUs
were mostly idle. It did not take long to see that everything was blocked
waiting on a futex and to identify where it was in glibc. It's only a
factor when malloc debugging is enabled so normally people would not see it.

The "regression" is because CPUs are reaching C6 as they should and there
is a delay when exiting it. This is behaving as designed and fixing this
would involve doing something stupid. Once the problem RPM was removed
ebizzy performed as expected. 3.13-rc7, the revert and forcing max_cstate=1
all have similar performance.

Sorry about the noise.

-- 
Mel Gorman
SUSE Labs
--
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/