linux-kernel - Re: [PATCH v1 2/2] perf/core: Add support for PMUs that can be read from any CPU

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Sat, 3 Mar 2018 16:41:13 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     skannan@...eaurora.org
Cc:     mark.rutland@....com, Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>, avilaj@...eaurora.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] perf/core: Add support for PMUs that can be read
 from any CPU

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