[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <4970CB6F.9000301@linux.vnet.ibm.com>
Date: Fri, 16 Jan 2009 10:01:19 -0800
From: Corey Ashford <cjashfor@...ux.vnet.ibm.com>
To: Andi Kleen <andi@...stfloor.org>
CC: Paul Mackerras <paulus@...ba.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
Thomas Gleixner <tglx@...utronix.de>,
Andrew Morton <akpm@...ux-foundation.org>,
Stephane Eranian <eranian@...glemail.com>,
Eric Dumazet <dada1@...mosbay.com>,
Robert Richter <robert.richter@....com>,
Arjan van de Ven <arjan@...radead.org>,
Peter Anvin <hpa@...or.com>,
"David S. Miller" <davem@...emloft.net>,
perfctr-devel@...ts.sourceforge.net, maynardj@...ibm.com
Subject: Re: [patch] Performance Counters for Linux, v4
Andi Kleen wrote:
> Paul Mackerras <paulus@...ba.org> writes:
>> The perf counter subsystem will, in Ingo's design, naturally try to
>> schedule as many counters and groups on as it can. Given a list of
>> counters/groups, it could start with the first and keep on trying to
>> add counters or groups while it can, essentially trying all possible
>> combinations until it either fills up all the hardware counters or
>> exhausts the possible combinations. If it moves all the
>> counters/groups that do fit on up to the head of the list, and then
>> rotates them to the back of the list when the timeslice expires, that
>> would probably be OK. In fact the computation about what set of
>> counters/groups to put on should be done when adding/removing a
>> counter/group and when the timeslice expires, rather than at context
>> switch time. (I'm talking about the list of part-time counters/groups
>> here, of course.)
>
> One issue is that PMU counts can cover more than one CPU. One example
> for this are the Uncore events on Nehalem (which cover a whole socket)
> or when you are in AnyThreads monitoring mode (then you get events
> from both SMT siblings in a core)
>
> With that you would need to examine other CPU's state at context switch
> time. Probably not a good idea for scalability.
>
> -Andi
>
Over time, it seems clear that we will see multi-core processor designs
with increasingly large uncore/nest facilities, so this could become
more and more of an issue.
- Corey
Corey Ashford
Software Engineer
IBM Linux Technology Center, Linux Toolchain
Beaverton, OR
503-578-3507
cjashfor@...ibm.com
--
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