linux-kernel - Re: [PATCH] perf/x86/intel/pt: Allow disabling branch tracing

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Date:   Mon, 06 Feb 2017 18:05:29 +0200
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        vince@...ter.net, eranian@...gle.com,
        Arnaldo Carvalho de Melo <acme@...radead.org>,
        Borislav Petkov <bp@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] perf/x86/intel/pt: Allow disabling branch tracing

Andi Kleen <andi@...stfloor.org> writes:

> Alexander Shishkin <alexander.shishkin@...ux.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/.

Regards,
--
Alex