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Message-ID: <ZV4qFtFctJ9emXvd@kernel.org>
Date: Wed, 22 Nov 2023 13:19:34 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Mark Rutland <mark.rutland@....com>
Cc: Hector Martin <marcan@...can.st>, Ian Rogers <irogers@...gle.com>,
Marc Zyngier <maz@...nel.org>,
Arnaldo Carvalho de Melo <acme@...hat.com>,
James Clark <james.clark@....com>,
linux-perf-users@...r.kernel.org,
LKML <linux-kernel@...r.kernel.org>,
Asahi Linux <asahi@...ts.linux.dev>
Subject: Re: [REGRESSION] Perf (userspace) broken on big.LITTLE systems since
v6.5
Em Wed, Nov 22, 2023 at 03:49:18PM +0000, Mark Rutland escreveu:
> On Wed, Nov 22, 2023 at 10:06:23AM -0300, Arnaldo Carvalho de Melo wrote:
> > The point is that "cycles" when prefixed with "pmu/" shouldn't be
> > considered "cycles" as HW/0, in that setting it is "cycles" for that
> > PMU.
> Exactly.
> > (but we only have "cpu_cycles" for at least the a53 and a72 PMUs I
> > have access in a Libre Computer rockchip 3399-pc hybrid board, if we use
> > it, then we get what we want/had before, see below):
> Both Cortex-A53 and Cortex-A72 have the common PMUv3 events, so they have
> "cpu_cycles" and "bus_cycles".
root@...-rk3399-pc:~# ls -la /sys/devices/*/events/*cycles
-r--r--r-- 1 root root 4096 Nov 22 12:35 /sys/devices/armv8_cortex_a53/events/bus_cycles
-r--r--r-- 1 root root 4096 Nov 22 12:35 /sys/devices/armv8_cortex_a53/events/cpu_cycles
-r--r--r-- 1 root root 4096 Nov 22 12:35 /sys/devices/armv8_cortex_a72/events/bus_cycles
-r--r--r-- 1 root root 4096 Nov 22 12:35 /sys/devices/armv8_cortex_a72/events/cpu_cycles
root@...-rk3399-pc:~#
But on x86, on a AMD machine:
⬢[acme@...lbox ~]$ ls -la /sys/devices/*/events/*cycles
-r--r--r--. 1 nobody nobody 4096 Nov 22 12:48 /sys/devices/cpu/events/cpu-cycles
⬢[acme@...lbox ~]$
And an Intel:
[acme@...co asahi]$ ls -la /sys/devices/*/events/*cycles
-r--r--r--. 1 root root 4096 Nov 22 13:11 /sys/devices/cpu/events/bus-cycles
-r--r--r--. 1 root root 4096 Nov 22 13:11 /sys/devices/cpu/events/cpu-cycles
-r--r--r--. 1 root root 4096 Nov 22 13:11 /sys/devices/cpu/events/ref-cycles
[acme@...co asahi]$
Slight difference with those - and _.
> The Apple PMUs that Hector and Marc anre using don't follow the PMUv3
> architecture, and just have a "cycles" event.
I see, and even being prefixed with the PMU name, as
"apple_icestorm_pmu/cycles/" it ends up trumping that and moving that to
(PERF_TYPE_HARDWARE, PERF_HW_CPU_CYCLES) instead of
(/sys/devices/apple_icestorm_pmu/events/type,
/sys/devices/apple_icestorm_pmu/events/cycles) as I noticed with:
sys_perf_event_open: pid 0 cpu -1 group_fd -1 flags 0x8perf_event_open({type=PERF_TYPE_HARDWARE, size=0 /* PERF_ATTR_SIZE_??? */, config=0x7<<32|PERF_COUNT_HW_CPU_CYCLES, sample_period=0, sample_type=0, read_format=0, disabled=1, precise_ip=0 /* arbitrary skid */, ...}, 0, -1, -1, PERF_FLAG_FD_CLOEXEC) = -1 ENOENT (No such file or directory)
I.e.:
type=PERF_TYPE_HARDWARE, config=0x7<<32|PERF_COUNT_HW_CPU_CYCLES
It should be:
type=/sys/devices/apple_icestorm_pmu/events/type, config=/sys/devices/apple_icestorm_pmu/events/cycles
That is the minimal patch to address the regression reported, even if
using some kludge to buy time for a longer term more elegant solution,
Ian?
> [...]
> > So what we need here seems to be to translate the generic term "cycles"
> > to "cpu_cycles" when a PMU is explicitely passed in the event name and
> > it doesn't have "cycles" and then just retry.
>
> I'm not sure we need to map that.
>
> My thinking is:
>
> * If the user asks for "cycles" without a PMU name, that should use the
> PERF_TYPE_HARDWARE cycles event. The ARM PMUs handle that correctly when the
> event is directed to them.
>
> * If the user asks for "${pmu}/cycles/", that should only use the "cycles"
> event in that PMU's namespace, not PERF_TYPE_HARDWARE.
And thus, armv8_cortex_a53/cycles/ and armv8_cortex_a72/cycles/ should
just fail as there is no "cycles" for that PMU, no fallback.
> * If we need a way so say "use the PERF_TYPE_HARDWARE cycles event on ${pmu}",
> then we should have a new syntax for that (e.g. as we have for raw events),
> e.g. it would be possible to have "pmu/hw:cycles/" or something like that.
>
> That way there's no ambiguity.
- Arnaldo
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