From: Neil Leeder <nleeder@codeaurora.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
WillDeacon <will.deacon@arm.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Mark Langsdorf <mlangsdo@redhat.com>,
Mark Salter <msalter@redhat.com>, Jon Masters <jcm@redhat.com>,
Timur Tabi <timur@codeaurora.org>,
cov@codeaurora.org, nleeder@codeaurora.org
Subject: Re: [PATCH 0/2] qcom: add l2 cache perf events driver
Date: Wed, 8 Jun 2016 11:21:16 -0400 [thread overview]
Message-ID: <f4fc5806-7cf0-28ea-08d5-9bb26dbd576a@codeaurora.org> (raw)
In-Reply-To: <20160606090416.GB6831@leverpostej>
On 6/6/2016 05:04 AM, Mark Rutland wrote:
> On Fri, Jun 03, 2016 at 05:03:30PM -0400, Neil Leeder wrote:
>> This adds a new dynamic PMU to the Perf Events framework to program
>> and control the L2 cache PMUs in some Qualcomm Technologies SOCs.
>>
>> The driver exports formatting and event information to sysfs so it can
>> be used by the perf user space tools with the syntax:
>> perf stat -e l2cache/event=0x42/
>>
>> One point to note is that there are certain combinations of events
>> which are invalid, and which are detected in event_add().
>
> Which combinations of events are invalid?
>
> Please elaborate.
>
>> Simply having event_add() fail would result in event_sched_in() making
>> it Inactive, treating it as over-allocation of counters, leading to
>> repeated attempts to allocate the events and ending up with a
>> statistical count. A solution for this situation is to turn the
>> conflicting event off in event_add(). This allows a single error
>> message to be generated, and no recurring attempts to re-add the
>> invalid event. In order for this to work, event_sched_in()
>> needs to detect that event_add() changed the state, and not override it
>> and force it to Inactive.
>
> For heterogeneous PMUs, we added the pmu::filter_match(event) callback
> for a similar purpose: preventing an event from being scheduled on a
> core which does not support that event, while allowing other events to
> be scheduled.
>
> So if you truly need to filter events, the infrastructure for doing so
> already exists.
>
> However, you will need to elaborate on "there are certain combinations
> of events which are invalid".
>
Qualcomm PMUs have events arranged in a matrix of rows and columns.
Only one event can be enabled from each column at once. So this isn't a
heterogeneous CPU issue, and it doesn't seem to fit into filter_match()
because it is not an absolute restriction that this event can't be
enabled on this cpu, it's related to the other events which have
already been enabled.
>> This patchset requires:
>> [PATCH] soc: qcom: provide mechanism for drivers to access L2 registers
>
> A link would be remarkably helpful.
http://archive.arm.linux.org.uk/lurker/message/20160603.205900.1970f20d.en.html
>
> Better would be to fold that patch into this series, as it's the only
> user, and both are helpful review context for the other.
>
The L2 PMU driver is the first user of the L2-accessors patch
but it won't be the only one, which is why I kept it separate.
> Thanks,
> Mark.
>
Neil
--
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.
next prev parent reply other threads:[~2016-06-08 15:21 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-03 21:03 [PATCH 0/2] qcom: add l2 cache perf events driver Neil Leeder
2016-06-03 21:03 ` [PATCH 1/2] perf: allow add to change event state Neil Leeder
2016-06-03 21:38 ` Peter Zijlstra
2016-06-03 21:03 ` [PATCH 2/2] soc: qcom: add l2 cache perf events driver Neil Leeder
2016-06-06 9:51 ` Mark Rutland
2016-06-08 15:16 ` Neil Leeder
2016-06-09 15:56 ` Mark Rutland
2016-06-09 19:41 ` Peter Zijlstra
2016-06-10 22:34 ` Neil Leeder
2016-06-06 9:04 ` [PATCH 0/2] " Mark Rutland
2016-06-08 15:21 ` Neil Leeder [this message]
2016-06-08 16:12 ` Mark Rutland
2016-06-08 19:29 ` Neil Leeder
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