Re: [PATCH 0/2] perf vendor events arm64: Add A720/A520 events/metrics
From: James Clark
Date: Thu Feb 20 2025 - 09:38:41 EST
On 20/02/2025 3:33 am, Yangyu Chen wrote:
On 19 Feb 2025, at 06:33, Ian Rogers <irogers@xxxxxxxxxx> wrote:
On Tue, Feb 18, 2025 at 2:19 PM Namhyung Kim <namhyung@xxxxxxxxxx <mailto:namhyung@xxxxxxxxxx>> wrote:
On Tue, Feb 18, 2025 at 09:30:23AM +0000, James Clark wrote:
On 18/02/2025 12:41 am, Ian Rogers wrote:
On Fri, Feb 14, 2025 at 2:02 AM James Clark <james.clark@xxxxxxxxxx> wrote:
On 14/02/2025 5:49 am, Yangyu Chen wrote:
On 14 Feb 2025, at 09:12, Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
Hello,
On Thu, Feb 13, 2025 at 11:11:01PM +0800, Yangyu Chen wrote:
This patchset adds the perf JSON files for the Cortex-A720 and Cortex-A520
processors. Some events have been tested on Raxda Orion 6 with Cix P1 SoC
(8xA720 + 4xA520) running mainline Kernel with ACPI mode.
I'm curious how the name of PMUs look like. It is cortex_a720 (or a520)?
The name of PMUs comes from Arm's documentation. I have included these
links in each patch.
I remember there's a logic to check the length of hex digits at the end.
Could you provide more details about this?
Ian, are you ok with this?
I think they wouldn't be merged because they're core PMUs, so should be
fine? Even though they would otherwise be merged because they're more
than 3 hex digits.
Do we know the PMU names? If they are cortex_a520 and cortex_a720 then
It will be "armv9_cortex_a720" from this line:
PMUV3_INIT_SIMPLE(armv9_cortex_a720)
I see, thanks!
this comment at least reads a little stale:
https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/pmus.c?h=perf-tools-next#n76
```
/*
* There is a '_{num}' suffix. For decimal suffixes any length
* will do, for hexadecimal ensure more than 2 hex digits so
* that S390's cpum_cf PMU doesn't match.
*/
```
James is right that core PMUs aren't put on the same list as uncore/other PMUs.
Ok, then I guess we're good.
I think you may be able to do things that look odd, like today the
"i915" PMU can be called just "i", I think the a520/a720 naming will
allow "armv9_cortex/cycles/" as an event name, then open it on two
PMUs if they are present. We may only show one PMU in perf list as
that code I think assumes they're the same PMU as they only differ by
suffix:
https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/pmus.c?h=perf-tools-next#n384
I can imagine aggregation possibly being broken, but I think that
works off the number of PMUs not the names of the PMUs, so it should
be okay. Probably the only thing broken that matter is perf list when
you have a BIG.little system with a520 and a720, this may be broken
with say a a53 and a72 today as both of those suffix lengths are >2,
but maybe they use the "armv8._pmuv3_0", "armv8._pmuv3_1", etc. naming
convention. I suspect the >2 here:
https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/pmus.c?h=perf-tools-next#n80
would still work and be correct if it were >4. If that changes then
this will also need to change:
https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/Documentation/ABI/testing/sysfs-bus-event_source-devices?h=perf-tools-next#n12
Thanks,
Ian
On my system, the names of PMUs are `armv8_pmuv3_0` and
`armv8_pmuv3_1`:
```
$ ls /sys/bus/event_source/devices/
armv8_pmuv3_0 armv8_pmuv3_1 breakpoint kprobe software tracepoint uprobe
```
I searched for ACPI DSDT on my platform, but there's no mention of
a720 or a520. I haven't delved into the PMU kernel driver yet.
Ah yeah, with ACPI you get those names instead.
Additionally, there's a more significant problem for aarch64
BIG.little platforms when two or more types of cores don't have the
same PMUs. The perf list can only display the core PMUs on core0
unless we use the PERF_CPUID env to override it. This is because
perf will only probe the first MIDR here:
https://github.com/torvalds/linux/blob/87a132e73910e8689902aed7f2fc229d6908383b/tools/perf/arch/arm64/util/header.c#L60
However, I think this doesn't block this patch for adding events and metrics?
Thanks,
Yangyu Chen
I don't think that's an issue because events are listed per PMU rather
than per CPU and that MIDR function does take a CPU struct. From my
testing the only thing stopping all PMUs from being listed was the
numeric suffix de-duplication.
Either way, no, it shouldn't affect your patch. But I'm also looking
into Ian's suggestion to improve it anyway.
Thanks,
Namhyung