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: <1194605991.6289.162.camel@twins>
Date:	Fri, 09 Nov 2007 11:59:51 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	eranian@....hp.com
Cc:	perfmon2-devel@...ts.sourceforge.net, perfmon@...ali.hpl.hp.com,
	linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: conflict between tickless and perfmon2

On Fri, 2007-11-09 at 02:44 -0800, Stephane Eranian wrote:
> Hello,
> 
> We have identified a conflict between TICKLESS (CONFIG_NO_HZ) and
> the current perfmon2 implementation. The problem impacts system-wide
> sessions using timeout-based event set multiplexing.
> 
> Event set multiplexing allows monitoring tools to measure more events
> than there are actual performance counters on the processor. Events
> are grouped in sets which are then multiplexed onto the actual counters.
> Switching can be triggered either by a timeout or by a counter overflow.
> This is supported for per-thread and system-wide sessions.
> 
> For timeout-based switching, the duration expressed in nanoseconds is
> meant to represent wall-clock time in system-wide mode, and execution
> time in per-thread mode. Granularity is limited by HZ.
> 
> The current implementation for timeout is a simple hook on the timer
> interrupt path in apic_*.c:smp_local_timer_interrupt(). Unfortunately,
> this does not work when tickless is enabled: we get much less set
> switches than expected on an idle system.
> 
> It looks like a solution would be to change the implementation of
> timeout-based switching to use HR timers instead. Similar to what is
> done for ITIMER_REAL and ITIMER_VIRTUAL.
> 
> Unless someone has a better proposal, I will experiment with this on
> 2.6.24-rc2.

Might help if you CC the tickless folks :-)

-
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/

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ