Re: [PATCH v8 4/5] arm64: arm_pmu: Add support for exclude_host/exclude_guest attributes

From: Suzuki K Poulose <suzuki.poulose@arm.com>
To: Andrew Murray <andrew.murray@arm.com>,
	Christoffer Dall <christoffer.dall@arm.com>,
	Marc Zyngier <marc.zyngier@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Mark Rutland <mark.rutland@arm.com>
Cc: kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org,
	Julien Thierry <julien.thierry@arm.com>
Subject: Re: [PATCH v8 4/5] arm64: arm_pmu: Add support for exclude_host/exclude_guest attributes
Date: Wed, 12 Dec 2018 10:55:33 +0000	[thread overview]
Message-ID: <f370a0fe-4a91-7e14-a7a5-aba25d0e7e52@arm.com> (raw)
In-Reply-To: <1544610573-28446-5-git-send-email-andrew.murray@arm.com>

On 12/12/2018 10:29, Andrew Murray wrote:
> Add support for the :G and :H attributes in perf by handling the
> exclude_host/exclude_guest event attributes.
> 
> We notify KVM of counters that we wish to be enabled or disabled on
> guest entry/exit and thus defer from starting or stopping :G events
> as per the events exclude_host attribute.
> 
> With both VHE and non-VHE we switch the counters between host/guest
> at EL2. We are able to eliminate counters counting host events on
> the boundaries of guest entry/exit when using :G by filtering out
> EL2 for exclude_host. However when using :H unless exclude_hv is set
> on non-VHE then there is a small blackout window at the guest
> entry/exit where host events are not captured.
> 
> Signed-off-by: Andrew Murray <andrew.murray@arm.com>
> ---
>   arch/arm64/kernel/perf_event.c | 51 ++++++++++++++++++++++++++++++++++++------
>   1 file changed, 44 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
> index de564ae..4a3c73d 100644
> --- a/arch/arm64/kernel/perf_event.c
> +++ b/arch/arm64/kernel/perf_event.c
> @@ -26,6 +26,7 @@
>   
>   #include <linux/acpi.h>
>   #include <linux/clocksource.h>
> +#include <linux/kvm_host.h>
>   #include <linux/of.h>
>   #include <linux/perf/arm_pmu.h>
>   #include <linux/platform_device.h>
> @@ -647,11 +648,26 @@ static inline int armv8pmu_enable_counter(int idx)
>   
>   static inline void armv8pmu_enable_event_counter(struct perf_event *event)
>   {
> +	struct perf_event_attr *attr = &event->attr;
>   	int idx = event->hw.idx;
> +	int flags = 0;
> +	u32 counter_bits = BIT(ARMV8_IDX_TO_COUNTER(idx));
>   
> -	armv8pmu_enable_counter(idx);
>   	if (armv8pmu_event_is_chained(event))
> -		armv8pmu_enable_counter(idx - 1);
> +		counter_bits |= BIT(ARMV8_IDX_TO_COUNTER(idx - 1));
> +
> +	if (!attr->exclude_host)
> +		flags |= KVM_PMU_EVENTS_HOST;
> +	if (!attr->exclude_guest)
> +		flags |= KVM_PMU_EVENTS_GUEST;
> +
> +	kvm_set_pmu_events(counter_bits, flags);
> +
> +	if (!attr->exclude_host) {
> +		armv8pmu_enable_counter(idx);
> +		if (armv8pmu_event_is_chained(event))
> +			armv8pmu_enable_counter(idx - 1);
> +	}
>   }
>   
>   static inline int armv8pmu_disable_counter(int idx)
> @@ -664,11 +680,20 @@ static inline int armv8pmu_disable_counter(int idx)
>   static inline void armv8pmu_disable_event_counter(struct perf_event *event)
>   {
>   	struct hw_perf_event *hwc = &event->hw;
> +	struct perf_event_attr *attr = &event->attr;
>   	int idx = hwc->idx;
> +	u32 counter_bits = BIT(ARMV8_IDX_TO_COUNTER(idx));
>   
>   	if (armv8pmu_event_is_chained(event))
> -		armv8pmu_disable_counter(idx - 1);
> -	armv8pmu_disable_counter(idx);
> +		counter_bits |= BIT(ARMV8_IDX_TO_COUNTER(idx - 1));
> +
> +	kvm_clr_pmu_events(counter_bits);
> +
> +	if (!attr->exclude_host) {
> +		if (armv8pmu_event_is_chained(event))
> +			armv8pmu_disable_counter(idx - 1);
> +		armv8pmu_disable_counter(idx);
> +	}

It may be helpful to add in a comment why we do this only for !exclude_host.

Either way,

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>

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