From mboxrd@z Thu Jan  1 00:00:00 1970
From: peterz@infradead.org (Peter Zijlstra)
Date: Sat, 3 Mar 2018 16:41:13 +0100
Subject: [PATCH v1 2/2] perf/core: Add support for PMUs that can be read
 from any CPU
In-Reply-To: <7cab1b91545e81e4b6b09e85c2f81d7e@codeaurora.org>
References: <1519431578-11995-1-git-send-email-skannan@codeaurora.org>
 <1519431578-11995-2-git-send-email-skannan@codeaurora.org>
 <20180224084106.GC25201@hirez.programming.kicks-ass.net>
 <7cab1b91545e81e4b6b09e85c2f81d7e@codeaurora.org>
Message-ID: <20180303154113.GH25201@hirez.programming.kicks-ass.net>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Mon, Feb 26, 2018 at 05:53:57PM -0800, skannan at 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...