linux-kernel - Re: [RFC PATCH 01/20] coresight: etm3x: splitting 'etm_enable

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Message-ID: <87y4fl3mt4.fsf@ashishki-desk.ger.corp.intel.com>
Date:	Fri, 02 Oct 2015 07:40:39 +0300
From:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:	Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:	Greg KH <gregkh@...uxfoundation.org>, a.p.zijlstra@...llo.nl,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...hat.com>, Jon Corbet <corbet@....net>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Chunyan Zhang <zhang.chunyan@...aro.org>,
	Mike Leach <mike.leach@....com>, Tor Jeremiassen <tor@...com>,
	Al Grant <al.grant@....com>,
	Paweł Moll <pawel.moll@....com>,
	"linux-arm-kernel\@lists.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, linux-doc@...r.kernel.org,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 01/20] coresight: etm3x: splitting 'etm_enable_hw()' operations

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

> On 30 September 2015 at 03:58, Alexander Shishkin
> <alexander.shishkin@...ux.intel.com> wrote:
>> Most of these things can also be bypassed, as at least initially perf
>> events won't be using trigger/sequencer configurations, so we could
>> simply clear all these things out when a first perf event is created
>> (which would also disallow any sysfs poking around the etm/etb) and not
>> worry about them in the pmu callbacks.
>
> I don't want to restrain configuration options to what is available
> through Perf's cmd line.  The sysFS interface is there to complement
> what is currently not available.

In practice this means that part of your trace configuration will be
global and part -- per event, which can indeed work if you only have one
event at a time, but again, makes using perf infrastructure redundant
for this driver. For multiple events this doesn't make much sense.

Regards,
--
Alex
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