linux-kernel - Re: [PATCH 1/3] perf, pt, coresight: Clean up address filter structure

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Message-ID: <87h94kbt29.fsf@ashishki-desk.ger.corp.intel.com>
Date:   Fri, 27 Jan 2017 14:12:14 +0200
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Mathieu Poirier <mathieu.poirier@...aro.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>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 1/3] perf, pt, coresight: Clean up address filter structure

Mathieu Poirier <mathieu.poirier@...aro.org> writes:

> Hi Alex,

Hi Mathieu,

> This changes the behavior we used to have.  Now a range filter with a size of 0
> will be treated as start filter rather than an error.  See below on a possible
> way of fixing this.

Not really. Currently we have 2 drivers using this and both reject the
type=range&&size==0 filters with either -EOPNOTSUPP or -EINVAL. With
this change, PT will still reject it as it doesn't support single
address triggers, but Coresight will treat it as if it was a single
address filter. Which makes sense, because that's what a range of size
zero is. Note, that a range that covers one instruction has to be at
least size==1 (and I'm guessing size==4 for Coresight, but I may be
wrong).

So yes, this does change the existing behavior, but in doing so it
removes the ambiguity of zero sized ranges.

>                         if (filter->action == PERF_ADDR_FILTER_ACTION_RANGE)

But "range" is not an action, it's a type of a filter. It determines the
condition that triggers an action. An action, however, is what we do
when the condition comes true.

Regards,
--
Alex