From: Suzuki K Poulose <Suzuki.Poulose@arm.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, will.deacon@arm.com,
robin.murphy@arm.com, julien.thierry@arm.com
Subject: Re: [PATCH v3 4/7] arm_pmu: Tidy up clear_event_idx call backs
Date: Fri, 29 Jun 2018 15:18:23 +0100 [thread overview]
Message-ID: <109b2082-f4ae-9095-7d6f-9daf78b38144@arm.com> (raw)
In-Reply-To: <20180629134049.b6sppasr7j32h37g@lakrids.cambridge.arm.com>
Hi Mark,
On 29/06/18 14:40, Mark Rutland wrote:
> On Tue, Jun 19, 2018 at 11:15:39AM +0100, Suzuki K Poulose wrote:
>> The armpmu uses get_event_idx callback to allocate an event
>> counter for a given event, which marks the selected counter
>> as "used". Now, when we delete the counter, the arm_pmu goes
>> ahead and clears the "used" bit and then invokes the "clear_event_idx"
>> call back, which kind of splits the job between the core code
>> and the backend. Tidy this up by relying on the clear_event_idx
>> to do the book keeping, if available. Otherwise, let the core
>> driver do the default "clear" bit operation. This will be useful
>> for adding the chained event support, where we leave the event
>> idx maintenance to the backend.
>>
>> Also, when an event is removed from the PMU, reset the hw.idx
>> to indicate that a counter is not allocated for this event,
>> to help the backends do better checks. This will be also used
>> for the chain counter support.
>>
>> Cc: Mark Rutland <mark.rutland@arm.com>
>> Cc: Will Deacon <will.deacon@arm.com>
>> Reviewed-by: Julien Thierry <julien.thierry@arm.com>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>> ---
>> Changes since v2:
>> - Reset the event counter after an event is removed.
>> ---
>> arch/arm/kernel/perf_event_v7.c | 2 ++
>> drivers/perf/arm_pmu.c | 17 +++++++++++++----
>> 2 files changed, 15 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm/kernel/perf_event_v7.c b/arch/arm/kernel/perf_event_v7.c
>> index fd7ce01..765d265 100644
>> --- a/arch/arm/kernel/perf_event_v7.c
>> +++ b/arch/arm/kernel/perf_event_v7.c
>> @@ -1637,6 +1637,7 @@ static void krait_pmu_clear_event_idx(struct pmu_hw_events *cpuc,
>> bool venum_event = EVENT_VENUM(hwc->config_base);
>> bool krait_event = EVENT_CPU(hwc->config_base);
>>
>> + clear_bit(hwc->idx, cpuc->used_mask);
>> if (venum_event || krait_event) {
>> bit = krait_event_to_bit(event, region, group);
>> clear_bit(bit, cpuc->used_mask);
>> @@ -1966,6 +1967,7 @@ static void scorpion_pmu_clear_event_idx(struct pmu_hw_events *cpuc,
>> bool venum_event = EVENT_VENUM(hwc->config_base);
>> bool scorpion_event = EVENT_CPU(hwc->config_base);
>>
>> + clear_bit(hwc->idx, cpuc->used_mask);
>> if (venum_event || scorpion_event) {
>> bit = scorpion_event_to_bit(event, region, group);
>> clear_bit(bit, cpuc->used_mask);
>
> As an aside, I think there's an existing problem with krait and
> cpu_pm_pmu_setup(), and we'll end up with the same issue when chained
> counters use multiple counters for one event.
>
> The krait code sets multiple bits in the PMU's pmu_hw_events::used_mask,
> but only one of these will have a corresponding (non-NULL) entry in
> pmu_hw_events::events[].
The Krait pmu allocates the "krait" specific event bit beyond the armpmu->num_events.
See krait_event_to_bit(). And we don't go beyond armpmu->num_events for the "events"
check. So we should be safe. And it passes on the idx within the num_events back
to armpmu. So whatever krait pmu does is invisible to the generic driver.
>
> In cpu_pm_pmu_setup(), when we find the auxilliary counter associated
> with an event, its bit will be set in used_mask, but the pointer will be
> NULL, and that will blow up in start/stop.
>
> We can't just set multiple slots to point at the same counter, or we'd
> try to start/stop an event multiple times, which would also be bad.
No, we don't. Since we cap the loops at armpmu->num_events.
>
> I guess the best thing to do would be to avoid the test_bit(), and just
> skip an idx if hw_events->events[idx] is NULL.
>
> Would you mind spinning a patch to that effect?
Eitherway, I could split that change to a new one.
Cheers
Suzuki
next prev parent reply other threads:[~2018-06-29 14:18 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-19 10:15 [PATCH v3 0/7] arm64: perf: Support for chained counters Suzuki K Poulose
2018-06-19 10:15 ` [PATCH v3 1/7] arm_pmu: Clean up maximum period handling Suzuki K Poulose
2018-06-19 10:45 ` Mark Rutland
2018-06-19 10:15 ` [PATCH v3 2/7] arm_pmu: Change API to support 64bit counter values Suzuki K Poulose
2018-06-19 10:52 ` Mark Rutland
2018-06-19 10:15 ` [PATCH v3 3/7] arm_pmu: Add support for 64bit event counters Suzuki K Poulose
2018-06-19 10:57 ` Mark Rutland
2018-06-19 10:15 ` [PATCH v3 4/7] arm_pmu: Tidy up clear_event_idx call backs Suzuki K Poulose
2018-06-29 13:27 ` Mark Rutland
2018-06-29 13:40 ` Mark Rutland
2018-06-29 14:18 ` Suzuki K Poulose [this message]
2018-06-29 14:29 ` Mark Rutland
2018-06-19 10:15 ` [PATCH v3 5/7] arm64: perf: Clean up armv8pmu_select_counter Suzuki K Poulose
2018-06-29 13:29 ` Mark Rutland
2018-06-19 10:15 ` [PATCH v3 6/7] arm64: perf: Disable PMU while processing counter overflows Suzuki K Poulose
2018-06-19 10:43 ` Mark Rutland
2018-06-19 10:15 ` [PATCH v3 7/7] arm64: perf: Add support for chaining event counters Suzuki K Poulose
2018-06-29 14:01 ` Mark Rutland
2018-06-29 14:29 ` Suzuki K Poulose
2018-06-29 14:39 ` Mark Rutland
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