From: Andi Kleen <andi@firstfloor.org>
To: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <andi@firstfloor.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, vince@deater.net,
eranian@google.com, Arnaldo Carvalho de Melo <acme@infradead.org>,
Borislav Petkov <bp@suse.de>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] perf/x86/intel/pt: Allow disabling branch tracing
Date: Mon, 6 Feb 2017 09:19:21 -0800 [thread overview]
Message-ID: <20170206171921.GG26852@two.firstfloor.org> (raw)
In-Reply-To: <87mvdz8fue.fsf@ashishki-desk.ger.corp.intel.com>
On Mon, Feb 06, 2017 at 06:05:29PM +0200, Alexander Shishkin wrote:
> Andi Kleen <andi@firstfloor.org> writes:
>
> > Alexander Shishkin <alexander.shishkin@linux.intel.com> writes:
> >
> >> Now that Intel PT supports more types of trace content than just branch
> >> tracing, it may be useful to allow the user to disable branch tracing
> >> when it is not needed.
> >>
> >> The special case is BDW, where not setting BranchEn is not supported.
> >>
> >> This is slightly trickier than necessary, because up to this moment
> >> the driver has been setting BranchEn automatically and the userspace
> >> assumes as much. Instead of reversing the semantics of BranchEn, we
> >> introduce a 'passthrough' bit, which will forego the default and allow
> >> the user to set BranchEn to their heart's content.
> >
> > cpu/passthrough=1,branchen=1/ seems far uglier/more complicanted to me
> > than the original cpu/nobranch=1/
>
> It's /passthrough=1,branch=0/ or simply /passthrough=1/.
Ok, but still you have to list exactly to which flags passthrough
applies to, and it will only ever be branchen.
So basically you turned nobranch=1 into two more difficult to
explain flags without any future advantage.
That is why nobranch=1 is better. It is far easier to explain
and logical to the user.
-Andi
next prev parent reply other threads:[~2017-02-06 17:19 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-27 15:16 [PATCH 0/2] perf/x86/intel/pt: Misc updates Alexander Shishkin
2017-01-27 15:16 ` [PATCH 1/2] perf/x86/intel/pt: Add format strings for PTWRITE and power event tracing Alexander Shishkin
2017-02-01 10:21 ` [tip:perf/core] " tip-bot for Alexander Shishkin
2017-01-27 15:16 ` [PATCH 2/2] perf/x86/intel/pt: Allow disabling branch tracing Alexander Shishkin
2017-02-01 10:17 ` Ingo Molnar
2017-02-01 16:49 ` Alexander Shishkin
2017-02-02 10:14 ` Alexander Shishkin
2017-02-06 14:41 ` [PATCH] " Alexander Shishkin
2017-02-06 15:58 ` Andi Kleen
2017-02-06 16:05 ` Alexander Shishkin
2017-02-06 17:19 ` Andi Kleen [this message]
2017-04-27 8:11 ` Adrian Hunter
2017-03-30 8:33 ` [tip:perf/core] perf/x86/intel/pt: Allow the disabling of " tip-bot for Alexander Shishkin
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