From: Jiri Olsa <jolsa@redhat.com>
To: Andi Kleen <ak@linux.intel.com>
Cc: linux-kernel@vger.kernel.org,
Arnaldo Carvalho de Melo <acme@redhat.com>,
Corey Ashford <cjashfor@linux.vnet.ibm.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
Ingo Molnar <mingo@elte.hu>, Paul Mackerras <paulus@samba.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Don Zickus <dzickus@redhat.com>,
Andi Kleen <ak@linux.jf.intel.com>,
Adrian Hunter <adrian.hunter@intel.com>,
Stephane Eranian <eranian@google.com>
Subject: Re: [RFC 00/21] perf tools: Add toggling events support
Date: Thu, 26 Sep 2013 14:11:55 +0200 [thread overview]
Message-ID: <20130926121154.GA1067@krava.brq.redhat.com> (raw)
In-Reply-To: <20130925191216.GE2018@tassilo.jf.intel.com>
On Wed, Sep 25, 2013 at 12:12:16PM -0700, Andi Kleen wrote:
> On Wed, Sep 25, 2013 at 02:50:26PM +0200, Jiri Olsa wrote:
> > hi,
> > sending *RFC* for toggling events support.
> >
> > Adding perf interface that allows to create toggle events, which can
> > enable or disable another event. Whenever the toggle event is triggered
> > (has overflow), it toggles another event state and either starts or
> > stops it.
> >
> > The goal is to be able to create toggling tracepoint events to enable and
> > disable HW counters, but the interface is generic enough to be used for
> > any kind of event.
>
> Haven't read the patches, but frequent full event switch in/out seems
> very expensive. If someone puts that switch on a common
> function it would likely disturb things quite a bit.
We dont do full sched in/out.. the toggled event
is scheduled in 'paused' state which means that
it's not started. Once the trigger is hit, pmu
start/stop is executed.
>
> It would be better to keep counting and just do RDPMC on
> the switch points, and then subtract for counting.
> For sampling could need a MSR write to enable/disable.
> Still somewhat expensive, but nowhere near as bad as a full switch.
I'll check on that
>
> Another problem is that it may be very inexact, as
> the counting will often happen in the background
> and not be very synchronized with the switches.
> Not fully sure how big a problem that would be.
the toggling overflow function does following
(perf_event_toggle_overflow)
- disable pmu of the toggled event
- start/stop the toggle event
- store sample for the trigger function
- enable pmu of the toggled event
so the overhead (extra count) is:
- the return code from pmu enable and return from the overflow processing
- trigger event overflow processing till pmu disable code
and no overhead for user space events ;-)
thanks,
jirka
next prev parent reply other threads:[~2013-09-26 12:12 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-25 12:50 Jiri Olsa
2013-09-25 12:50 ` [PATCH 01/21] perf tools: Introduce perf_evlist__wait_workload function Jiri Olsa
2013-09-25 12:50 ` [PATCH 02/21] perf tools: Separate sys_perf_event_open call into evsel_open Jiri Olsa
2013-09-25 12:50 ` [PATCH 03/21] perf x86: Update event count properly for read syscall Jiri Olsa
2013-09-25 12:50 ` [PATCH 04/21] perf: Move event state initialization before/behind the pmu add/del calls Jiri Olsa
2013-09-25 12:50 ` [PATCH 05/21] perf: Add event toggle sys_perf_event_open interface Jiri Olsa
2013-09-25 22:36 ` Sukadev Bhattiprolu
2013-09-26 12:27 ` Jiri Olsa
2013-09-25 12:50 ` [PATCH 06/21] perf: Add event toggle ioctl interface Jiri Olsa
2013-09-25 19:46 ` Vince Weaver
2013-09-26 12:30 ` Jiri Olsa
2013-09-26 13:03 ` Vince Weaver
2013-09-25 12:50 ` [PATCH 07/21] perf: Toggle whole group in toggle event overflow Jiri Olsa
2013-09-25 12:50 ` [PATCH 08/21] perf: Add new 'paused' attribute Jiri Olsa
2013-09-25 22:41 ` Sukadev Bhattiprolu
2013-09-26 12:24 ` Jiri Olsa
2013-09-25 12:50 ` [PATCH 09/21] perf: Account toggle masters for toggled event Jiri Olsa
2013-09-25 12:50 ` [PATCH 10/21] perf: Be more specific on pmu related event init naming Jiri Olsa
2013-09-25 12:50 ` [PATCH 11/21] perf: Split allocation and initialization code Jiri Olsa
2013-09-25 12:50 ` [PATCH 12/21] perf: Support event inheritance for toggle feature Jiri Olsa
2013-09-25 12:50 ` [PATCH 13/21] perf tests: Adding event simple toggling test Jiri Olsa
2013-09-25 12:50 ` [PATCH 14/21] perf tests: Adding event group " Jiri Olsa
2013-09-25 12:50 ` [PATCH 15/21] perf tests: Adding event inherit " Jiri Olsa
2013-09-25 12:50 ` [PATCH 16/21] perf tools: Allow numeric event to change name via name term Jiri Olsa
2013-09-25 12:50 ` [PATCH 17/21] perf tools: Add event_config_optional parsing rule Jiri Olsa
2013-09-25 12:50 ` [PATCH 18/21] perf tools: Rename term related parsing function/variable properly Jiri Olsa
2013-09-25 12:50 ` [PATCH 19/21] perf tools: Carry term string value for symbols events Jiri Olsa
2013-09-25 12:50 ` [PATCH 20/21] perf tools: Add support to parse event on/off toggle terms Jiri Olsa
2013-09-25 12:50 ` [PATCH 21/21] perf tools: Add record/stat support for toggling events Jiri Olsa
2013-09-25 19:12 ` [RFC 00/21] perf tools: Add toggling events support Andi Kleen
2013-09-26 7:03 ` Ingo Molnar
2013-09-26 15:45 ` Andi Kleen
2013-09-26 12:11 ` Jiri Olsa [this message]
2013-09-26 11:31 ` Stephane Eranian
2013-09-26 12:20 ` Jiri Olsa
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