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Date: Sat, 3 Mar 2018 16:41:13 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: skannan@codeaurora.org
Cc: mark.rutland@arm.com, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
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Subject: Re: [PATCH v1 2/2] perf/core: Add support for PMUs that can be read
 from any CPU
Message-ID: <20180303154113.GH25201@hirez.programming.kicks-ass.net>
References: <1519431578-11995-1-git-send-email-skannan@codeaurora.org>
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On Mon, Feb 26, 2018 at 05:53:57PM -0800, skannan@codeaurora.org wrote:
> On 2018-02-24 00:41, Peter Zijlstra wrote:
> > On Fri, Feb 23, 2018 at 04:19:38PM -0800, Saravana Kannan wrote:
> > > Some PMUs events can be read from any CPU. So allow the PMU to mark
> > > events as such. For these events, we don't need to reject reads or
> > > make smp calls to the event's CPU and cause unnecessary wake ups.
> > > 
> > > Good examples of such events would be events from caches shared across
> > > all CPUs.
> > 
> > So why would the existing ACTIVE_PKG not work for you? Because clearly
> > your example does not cross a package.
> 
> Because based on testing it on hardware, it looks like the two clusters in
> an ARM DynamIQ design are not considered part of the same "package". When I
> say clusters, I using the more common interpretation of "homogeneous CPUs
> running on the same clock"/CPUs in a cpufreq policy and not ARM's new
> redefinition of cluster. So, on a SoC with 4 little and 4 big cores, it'll
> still trigger a lot of unnecessary smp calls/IPIs that cause unnecessary
> wakeups.

arch/arm64/include/asm/topology.h:#define topology_physical_package_id(cpu)     (cpu_topology[cpu].cluster_id)

*sigh*... that's just broken...