Messages in this thread | | | From | Anshuman Khandual <> | Subject | Re: [RFC V1 03/11] arm64/perf: Update struct arm_pmu for BRBE | Date | Fri, 28 Jan 2022 09:08:20 +0530 |
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On 1/26/22 10:29 PM, Rob Herring wrote: > On Mon, Jan 24, 2022 at 10:00:45AM +0530, Anshuman Khandual wrote: >> This updates struct arm_pmu to include all required helpers that will drive > >>From submitting-patches.rst: > > Describe your changes in imperative mood, e.g. "make xyzzy do frotz" > instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy > to do frotz", as if you are giving orders to the codebase to change > its behaviour.
s/This updates struct arm_pmu to/Update struct arm_pmu to/ should address this problem I guess. Although the difference here seems very subtle :)
> >> BRBE functionality for a given PMU implementation. These are the following. > > Don't describe what the change is, one can read the diff for that.
Sure, though was trying just to enumerate a potential driver's functional responsibilities.
> Answer why it is needed.
Sure.
> > One thing to answer in the commit msg is why we need the hooks here. > Have we concluded that adding BRBE hooks to struct arm_pmu for what is > an armv8 specific feature is the right approach? I don't recall > reaching that conclusion.
Although it might be possible to have this implementation embedded in the existing armv8 PMU implementation, I still believe that the BRBE functionalities abstracted out at the arm_pmu level with a separate config option is cleaner, easier to follow and to maintain as well.
Besides some helpers i.e brbe_supported(), brbe_probe() and brbe_reset() might not fit seamlessly, when tried to be embedded via existing arm_pmu helpers in the armv8 implementation.
Nonetheless if arm_pmu based additional BRBE helpers is absolutely a no go for folks here in general, will explore arm64 based implementation.
> >> >> - brbe_filter : Convert perf event filters into BRBE HW filters >> - brbe_probe : Probe BRBE HW and capture its attributes >> - brbe_enable : Enable BRBE HW with a given config >> - brbe_disable : Disable BRBE HW >> - brbe_read : Read BRBE buffer for captured branch records >> - brbe_reset : Reset BRBE buffer >> - brbe_supported: Whether BRBE is supported or not > > The function names seem pretty self-explanatory, but the text is needed, > shouldn't it be in the struct declaration.
Sure, sounds good. Will move there.
> > I'm not really a fan of patches adding dead code. That's not any less to > review. Restructuring with 'no functional change' OTOH is helpful in > reviewing.
Restructuring without functional change clarifies the purpose better. Besides this is more relevant in this context where the functions will be provided by a separate (and also detached) driver implementation.
>> A BRBE driver implementation needs to provide these functionalities. >> >> Cc: Will Deacon <will@kernel.org> >> Cc: Mark Rutland <mark.rutland@arm.com> >> Cc: Peter Zijlstra <peterz@infradead.org> >> Cc: Ingo Molnar <mingo@redhat.com> >> Cc: Catalin Marinas <catalin.marinas@arm.com> >> Cc: linux-arm-kernel@lists.infradead.org >> Cc: linux-perf-users@vger.kernel.org >> Cc: linux-kernel@vger.kernel.org >> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> >> --- >> arch/arm64/kernel/perf_event.c | 36 ++++++++++++++++++++++++++++++++++ >> include/linux/perf/arm_pmu.h | 7 +++++++ >> 2 files changed, 43 insertions(+) >> >> diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c >> index cab678ed6618..f6a47036b0b4 100644 >> --- a/arch/arm64/kernel/perf_event.c >> +++ b/arch/arm64/kernel/perf_event.c >> @@ -1015,6 +1015,35 @@ static int armv8pmu_filter_match(struct perf_event *event) >> return evtype != ARMV8_PMUV3_PERFCTR_CHAIN; >> } >> >> +static void armv8pmu_brbe_filter(struct pmu_hw_events *hw_event, struct perf_event *event) >> +{ >> +} >> + >> +static void armv8pmu_brbe_enable(struct pmu_hw_events *hw_event) >> +{ >> +} >> + >> +static void armv8pmu_brbe_disable(struct pmu_hw_events *hw_event) >> +{ >> +} >> + >> +static void armv8pmu_brbe_read(struct pmu_hw_events *hw_event, struct perf_event *event) >> +{ >> +} >> + >> +static void armv8pmu_brbe_probe(struct pmu_hw_events *hw_event) >> +{ >> +} >> + >> +static void armv8pmu_brbe_reset(struct pmu_hw_events *hw_event) >> +{ >> +} >> + >> +static bool armv8pmu_brbe_supported(struct perf_event *event) >> +{ >> + return false; >> +} >> + >> static void armv8pmu_reset(void *info) >> { >> struct arm_pmu *cpu_pmu = (struct arm_pmu *)info; >> @@ -1247,6 +1276,13 @@ static int armv8_pmu_init(struct arm_pmu *cpu_pmu, char *name, >> >> cpu_pmu->pmu.event_idx = armv8pmu_user_event_idx; >> >> + cpu_pmu->brbe_filter = armv8pmu_brbe_filter; >> + cpu_pmu->brbe_enable = armv8pmu_brbe_enable; >> + cpu_pmu->brbe_disable = armv8pmu_brbe_disable; >> + cpu_pmu->brbe_read = armv8pmu_brbe_read; >> + cpu_pmu->brbe_probe = armv8pmu_brbe_probe; >> + cpu_pmu->brbe_reset = armv8pmu_brbe_reset; >> + cpu_pmu->brbe_supported = armv8pmu_brbe_supported; >> cpu_pmu->name = name; >> cpu_pmu->map_event = map_event; >> cpu_pmu->attr_groups[ARMPMU_ATTR_GROUP_EVENTS] = events ? >> diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h >> index 2512e2f9cd4e..c0dd0d6c5883 100644 >> --- a/include/linux/perf/arm_pmu.h >> +++ b/include/linux/perf/arm_pmu.h >> @@ -98,6 +98,13 @@ struct arm_pmu { >> void (*reset)(void *); >> int (*map_event)(struct perf_event *event); >> int (*filter_match)(struct perf_event *event); >> + void (*brbe_filter)(struct pmu_hw_events *hw_events, struct perf_event *event); >> + void (*brbe_probe)(struct pmu_hw_events *hw_events); >> + void (*brbe_enable)(struct pmu_hw_events *hw_events); >> + void (*brbe_disable)(struct pmu_hw_events *hw_events); >> + void (*brbe_read)(struct pmu_hw_events *hw_events, struct perf_event *event); >> + void (*brbe_reset)(struct pmu_hw_events *hw_events); >> + bool (*brbe_supported)(struct perf_event *event); >> int num_events; >> bool secure_access; /* 32-bit ARM only */ >> #define ARMV8_PMUV3_MAX_COMMON_EVENTS 0x40 >> -- >> 2.25.1 >> >>
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