From: Andi Kleen <ak@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: kan.liang@intel.com, mingo@redhat.com, acme@kernel.org,
linux-kernel@vger.kernel.org, tglx@linutronix.de,
eranian@google.com, jolsa@kernel.org
Subject: Re: [PATCH 1/3] perf/x86: add sysfs entry to freeze counter on SMI
Date: Thu, 23 Mar 2017 15:23:03 -0700 [thread overview]
Message-ID: <20170323222303.GA9371@tassilo.jf.intel.com> (raw)
In-Reply-To: <20170323203138.li45llrzfxcaqieu@hirez.programming.kicks-ass.net>
On Thu, Mar 23, 2017 at 09:31:38PM +0100, Peter Zijlstra wrote:
> On Thu, Mar 23, 2017 at 11:25:49AM -0700, kan.liang@intel.com wrote:
> > From: Kan Liang <Kan.liang@intel.com>
> >
> > When setting FREEZE_WHILE_SMM bit in IA32_DEBUGCTL, all performance
> > counters will be effected. There is no way to do per-counter freeze
> > on smi. So it should not use the per-event interface (e.g. ioctl or
> > event attribute) to set FREEZE_WHILE_SMM bit.
> >
> > Adds sysfs entry /sys/device/cpu/freeze_on_smi to set FREEZE_WHILE_SMM
> > bit in IA32_DEBUGCTL. When set, freezes perfmon and trace messages
> > while in SMM.
> > Value has to be 0 or 1. It will be applied to all possible cpus.
>
> So is there ever a good reason to not set this?
That means SMIs become invisible to most performance counters.
I don't think that's a good default. If the SMI takes 1% of my
cycles I want to see it.
The masking trick is mainly useful when doing --smi-cost
-Andi
next prev parent reply other threads:[~2017-03-23 22:23 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-23 18:25 [PATCH 0/3]measure SMI cost kan.liang
2017-03-23 18:25 ` [PATCH 1/3] perf/x86: add sysfs entry to freeze counter on SMI kan.liang
2017-03-23 20:31 ` Peter Zijlstra
2017-03-23 20:48 ` Liang, Kan
2017-03-23 22:23 ` Andi Kleen [this message]
2017-03-24 8:16 ` Peter Zijlstra
2017-03-23 20:32 ` Peter Zijlstra
2017-03-24 8:31 ` Thomas Gleixner
2017-03-24 14:15 ` Liang, Kan
2017-03-24 14:23 ` Peter Zijlstra
2017-03-23 18:25 ` [PATCH 2/3] tools lib api fs: Add sysfs__write_int function kan.liang
2017-03-28 3:38 ` Elliott, Robert (Persistent Memory)
2017-03-23 18:25 ` [PATCH 3/3] perf stat: Add support to measure SMI cost kan.liang
2017-03-24 8:44 ` [PATCH 0/3]measure " Thomas Gleixner
2017-03-24 11:40 ` Andi Kleen
2017-03-24 12:07 ` Thomas Gleixner
2017-03-24 14:14 ` Liang, Kan
2017-03-31 21:51 ` Stephane Eranian
2017-04-01 1:41 ` Liang, Kan
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