[PATCH v2] KVM/arm64: reconfigurate the event filters for guest context
Shijie Huang
shijie at amperemail.onmicrosoft.com
Fri Aug 11 01:16:20 PDT 2023
Hi Marc,
在 2023/8/11 15:56, Marc Zyngier 写道:
> On Fri, 11 Aug 2023 08:52:40 +0100,
> Shijie Huang <shijie at amperemail.onmicrosoft.com> wrote:
>> Hi Marc,
>>
>> 在 2023/8/11 15:42, Marc Zyngier 写道:
>>> On Fri, 11 Aug 2023 08:10:26 +0100,
>>> Shijie Huang <shijie at amperemail.onmicrosoft.com> wrote:
>>>> Hi Marc,
>>>>
>>>> 在 2023/8/11 14:10, Marc Zyngier 写道:
>>>>> On Fri, 11 Aug 2023 02:46:49 +0100,
>>>>> Shijie Huang <shijie at amperemail.onmicrosoft.com> wrote:
>>>>>> Hi Marc,
>>>>>>
>>>>>> 在 2023/8/10 23:27, Marc Zyngier 写道:
>>>>>>> Huang,
>>>>>>>
>>>>>>> Please make sure you add everyone who commented on v1 (I've Cc'd Mark
>>>>>>> so that he can shime need as needed).
>>>>>> thanks.
>>>>>>> On Thu, 10 Aug 2023 08:29:06 +0100,
>>>>>>> Huang Shijie <shijie at os.amperecomputing.com> wrote:
>>>>>>>> 1.) Background.
>>>>>>>> 1.1) In arm64, start a guest with Qemu which is running as a VMM of KVM,
>>>>>>>> and bind the guest to core 33 and run program "a" in guest.
>>>>>>>> The code of "a" shows below:
>>>>>>>> ----------------------------------------------------------
>>>>>>>> #include <stdio.h>
>>>>>>>>
>>>>>>>> int main()
>>>>>>>> {
>>>>>>>> unsigned long i = 0;
>>>>>>>>
>>>>>>>> for (;;) {
>>>>>>>> i++;
>>>>>>>> }
>>>>>>>>
>>>>>>>> printf("i:%ld\n", i);
>>>>>>>> return 0;
>>>>>>>> }
>>>>>>>> ----------------------------------------------------------
>>>>>>>>
>>>>>>>> 1.2) Use the following perf command in host:
>>>>>>>> #perf stat -e cycles:G,cycles:H -C 33 -I 1000 sleep 1
>>>>>>>> # time counts unit events
>>>>>>>> 1.000817400 3,299,471,572 cycles:G
>>>>>>>> 1.000817400 3,240,586 cycles:H
>>>>>>>>
>>>>>>>> This result is correct, my cpu's frequency is 3.3G.
>>>>>>>>
>>>>>>>> 1.3) Use the following perf command in host:
>>>>>>>> #perf stat -e cycles:G,cycles:H -C 33 -d -d -I 1000 sleep 1
>>>>>>>> time counts unit events
>>>>>>>> 1.000831480 153,634,097 cycles:G (70.03%)
>>>>>>>> 1.000831480 3,147,940,599 cycles:H (70.03%)
>>>>>>>> 1.000831480 1,143,598,527 L1-dcache-loads (70.03%)
>>>>>>>> 1.000831480 9,986 L1-dcache-load-misses # 0.00% of all L1-dcache accesses (70.03%)
>>>>>>>> 1.000831480 <not supported> LLC-loads
>>>>>>>> 1.000831480 <not supported> LLC-load-misses
>>>>>>>> 1.000831480 580,887,696 L1-icache-loads (70.03%)
>>>>>>>> 1.000831480 77,855 L1-icache-load-misses # 0.01% of all L1-icache accesses (70.03%)
>>>>>>>> 1.000831480 6,112,224,612 dTLB-loads (70.03%)
>>>>>>>> 1.000831480 16,222 dTLB-load-misses # 0.00% of all dTLB cache accesses (69.94%)
>>>>>>>> 1.000831480 590,015,996 iTLB-loads (59.95%)
>>>>>>>> 1.000831480 505 iTLB-load-misses # 0.00% of all iTLB cache accesses (59.95%)
>>>>>>>>
>>>>>>>> This result is wrong. The "cycle:G" should be nearly 3.3G.
>>>>>>>>
>>>>>>>> 2.) Root cause.
>>>>>>>> There is only 7 counters in my arm64 platform:
>>>>>>>> (one cycle counter) + (6 normal counters)
>>>>>>>>
>>>>>>>> In 1.3 above, we will use 10 event counters.
>>>>>>>> Since we only have 7 counters, the perf core will trigger
>>>>>>>> multiplexing in hrtimer:
>>>>>>>> perf_mux_hrtimer_restart() --> perf_rotate_context().
>>>>>>>>
>>>>>>>> If the hrtimer occurs when the host is running, it's fine.
>>>>>>>> If the hrtimer occurs when the guest is running,
>>>>>>>> the perf_rotate_context() will program the PMU with filters for
>>>>>>>> host context. The KVM does not have a chance to restore
>>>>>>>> PMU registers with kvm_vcpu_pmu_restore_guest().
>>>>>>>> The PMU does not work correctly, so we got wrong result.
>>>>>>>>
>>>>>>>> 3.) About this patch.
>>>>>>>> Make a KVM_REQ_RELOAD_PMU request before reentering the
>>>>>>>> guest. The request will call kvm_vcpu_pmu_restore_guest()
>>>>>>>> to reconfigurate the filters for guest context.
>>>>>>>>
>>>>>>>> 4.) Test result of this patch:
>>>>>>>> #perf stat -e cycles:G,cycles:H -C 33 -d -d -I 1000 sleep 1
>>>>>>>> time counts unit events
>>>>>>>> 1.001006400 3,298,348,656 cycles:G (70.03%)
>>>>>>>> 1.001006400 3,144,532 cycles:H (70.03%)
>>>>>>>> 1.001006400 941,149 L1-dcache-loads (70.03%)
>>>>>>>> 1.001006400 17,937 L1-dcache-load-misses # 1.91% of all L1-dcache accesses (70.03%)
>>>>>>>> 1.001006400 <not supported> LLC-loads
>>>>>>>> 1.001006400 <not supported> LLC-load-misses
>>>>>>>> 1.001006400 1,101,889 L1-icache-loads (70.03%)
>>>>>>>> 1.001006400 121,638 L1-icache-load-misses # 11.04% of all L1-icache accesses (70.03%)
>>>>>>>> 1.001006400 1,031,228 dTLB-loads (70.03%)
>>>>>>>> 1.001006400 26,952 dTLB-load-misses # 2.61% of all dTLB cache accesses (69.93%)
>>>>>>>> 1.001006400 1,030,678 iTLB-loads (59.94%)
>>>>>>>> 1.001006400 338 iTLB-load-misses # 0.03% of all iTLB cache accesses (59.94%)
>>>>>>>>
>>>>>>>> The result is correct. The "cycle:G" is nearly 3.3G now.
>>>>>>>>
>>>>>>>> Signed-off-by: Huang Shijie <shijie at os.amperecomputing.com>
>>>>>>>> ---
>>>>>>>> v1 --> v2:
>>>>>>>> Do not change perf/core code, only change the ARM64 kvm code.
>>>>>>>> v1: https://lkml.org/lkml/2023/8/8/1465
>>>>>>>>
>>>>>>>> ---
>>>>>>>> arch/arm64/kvm/arm.c | 11 ++++++++++-
>>>>>>>> 1 file changed, 10 insertions(+), 1 deletion(-)
>>>>>>>>
>>>>>>>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>>>>>>>> index c2c14059f6a8..475a2f0e0e40 100644
>>>>>>>> --- a/arch/arm64/kvm/arm.c
>>>>>>>> +++ b/arch/arm64/kvm/arm.c
>>>>>>>> @@ -919,8 +919,17 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
>>>>>>>> if (!ret)
>>>>>>>> ret = 1;
>>>>>>>> - if (ret > 0)
>>>>>>>> + if (ret > 0) {
>>>>>>>> + /*
>>>>>>>> + * The perf_rotate_context() may rotate the events and
>>>>>>>> + * reprogram PMU with filters for host context.
>>>>>>>> + * So make a request before reentering the guest to
>>>>>>>> + * reconfigurate the event filters for guest context.
>>>>>>>> + */
>>>>>>>> + kvm_make_request(KVM_REQ_RELOAD_PMU, vcpu);
>>>>>>>> +
>>>>>>>> ret = check_vcpu_requests(vcpu);
>>>>>>>> + }
>>>>>>> This looks extremely heavy handed. You're performing the reload on
>>>>>>> *every* entry, and I don't think this is right (exit-heavy workloads
>>>>>>> will suffer from it)
>>>>>>>
>>>>>>> Furthermore, you're also reloading the virtual state of the PMU
>>>>>>> (recreating guest events and other things), all of which looks pretty
>>>>>>> pointless, as all we're interested in is what is being counted on the
>>>>>>> *host*.
>>>>>> okay. What about to add a _new_ request, such as KVM_REQ_RESTROE_PMU_GUEST?
>>>>>>
>>>>>>
>>>>>>> Instead, we can restrict the reload of the host state (and only that)
>>>>>>> to situations where:
>>>>>>>
>>>>>>> - we're running on a VHE system
>>>>>>>
>>>>>>> - we have a host PMUv3 (not everybody does), as that's the only way we
>>>>>>> can profile a guest
>>>>>> okay. No problem.
>>>>>>
>>>>>>
>>>>>>> and ideally we would have a way to detect that a rotation happened
>>>>>>> (which may requires some help from the low-level PMU code).
>>>>>> I will check it, hope we can find a better way.
>>>>> I came up with the following patch, completely untested. Let me know
>>>>> how that fares for you.
>>>>>
>>>>> Thanks,
>>>>>
>>>>> M.
>>>>>
>>>>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
>>>>> index 93c541111dea..fb875c5c0347 100644
>>>>> --- a/arch/arm64/include/asm/kvm_host.h
>>>>> +++ b/arch/arm64/include/asm/kvm_host.h
>>>>> @@ -49,6 +49,7 @@
>>>>> #define KVM_REQ_RELOAD_GICv4 KVM_ARCH_REQ(4)
>>>>> #define KVM_REQ_RELOAD_PMU KVM_ARCH_REQ(5)
>>>>> #define KVM_REQ_SUSPEND KVM_ARCH_REQ(6)
>>>>> +#define KVM_REQ_RELOAD_GUEST_PMU_EVENTS KVM_ARCH_REQ(7)
>>>>> #define KVM_DIRTY_LOG_MANUAL_CAPS
>>>>> (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE | \
>>>>> KVM_DIRTY_LOG_INITIALLY_SET)
>>>>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>>>>> index 8b51570a76f8..b40db24f1f0b 100644
>>>>> --- a/arch/arm64/kvm/arm.c
>>>>> +++ b/arch/arm64/kvm/arm.c
>>>>> @@ -804,6 +804,9 @@ static int check_vcpu_requests(struct kvm_vcpu *vcpu)
>>>>> kvm_pmu_handle_pmcr(vcpu,
>>>>> __vcpu_sys_reg(vcpu, PMCR_EL0));
>>>>> + if (kvm_check_request(KVM_REQ_RELOAD_GUEST_PMU_EVENTS,
>>>>> vcpu))
>>>>> + kvm_vcpu_pmu_restore_guest(vcpu);
>>>>> +
>>>>> if (kvm_check_request(KVM_REQ_SUSPEND, vcpu))
>>>>> return kvm_vcpu_suspend(vcpu);
>>>>> diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c
>>>>> index 08b3a1bf0ef6..7012de417092 100644
>>>>> --- a/drivers/perf/arm_pmuv3.c
>>>>> +++ b/drivers/perf/arm_pmuv3.c
>>>>> @@ -772,6 +772,9 @@ static void armv8pmu_start(struct arm_pmu *cpu_pmu)
>>>>> /* Enable all counters */
>>>>> armv8pmu_pmcr_write(armv8pmu_pmcr_read() | ARMV8_PMU_PMCR_E);
>>>>> +
>>>>> + if (in_interrupt())
>>>>> + kvm_resync_guest_context();
>>>> I currently added a similiar check in armv8pmu_get_event_idx().
>>>>
>>>> The event multiplexing will call armv8pmu_get_event_idx(), and will
>>>> definitely fail at least one time.
>>>>
>>>> +++ b/drivers/perf/arm_pmuv3.c
>>>> @@ -882,6 +882,8 @@ static int armv8pmu_get_event_idx(struct
>>>> pmu_hw_events *cpuc,
>>>> struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu);
>>>> struct hw_perf_event *hwc = &event->hw;
>>>> unsigned long evtype = hwc->config_base & ARMV8_PMU_EVTYPE_EVENT;
>>>> + struct kvm_vcpu *vcpu;
>>>> + int index;
>>>> struct arm_pmu *cpu_pmu = to_arm_pmu(event->pmu);
>>>> struct hw_perf_event *hwc = &event->hw;
>>>> unsigned long evtype = hwc->config_base & ARMV8_PMU_EVTYPE_EVENT;
>>>> + struct kvm_vcpu *vcpu;
>>>> + int index;
>>>>
>>>> /* Always prefer to place a cycle counter into the cycle
>>>> counter. */
>>>> if (evtype == ARMV8_PMUV3_PERFCTR_CPU_CYCLES) {
>>>> @@ -897,9 +899,22 @@ static int armv8pmu_get_event_idx(struct
>>>> pmu_hw_events *cpuc,
>>>> * Otherwise use events counters
>>>> */
>>>> if (armv8pmu_event_is_chained(event))
>>>> - return armv8pmu_get_chain_idx(cpuc, cpu_pmu);
>>>> + index = armv8pmu_get_chain_idx(cpuc, cpu_pmu);
>>>> else
>>>> - return armv8pmu_get_single_idx(cpuc, cpu_pmu);
>>>> + index = armv8pmu_get_single_idx(cpuc, cpu_pmu);
>>>> +
>>>> + /*
>>>> + * If we are in pmu multiplexing, we will definitely meet a failure.
>>>> + * Please see perf_rotate_context().
>>>> + * If we are in the guest context, we can mark it.
>>>> + */
>>>> + if (index < 0) {
>>>> + vcpu = kvm_get_running_vcpu();
>>>> + if (vcpu && in_interrupt() && !event->attr.pinned) {
>>>> + kvm_resync_guest_context();
>> xxxx.
>>
>>
>>>> + }
>>>> + }
>>>> + return index;
>>>> }
>>>>
>>>> IMHO, it's better to change armv8pmu_get_event_idx().
>>>>
>>>> But if you think it is also okay to change armv8pmu_start() to fix the bug,
>>>>
>>>> I am okay too.
>>> But that's doing work each time you rotate an event. And if you rotate
>>> a bunch of them, you'll hit this path multiple times, reloading the
>>> stuff again. What's the point?
>> In my code, I just put the kvm_make_request() in "xxx" above. Event
>> reloading it multiple times,
>>
>> it just set a bit in vcpu->requests.
>>
>>
>>> My take is that we can hook at the point where the PMU gets
>>> re-enabled, and have the full context once and for all.
>>>
>>> Unless of course I miss something, which is very likely as the whole
>>> perf subsystem generally escapes me altogether.
>>>
>>> In any case, I'd welcome your testing the proposed patch.
>> No problem.
> As Oliver pointed out offline, I only have posted half of the patch...
>
> Here is the whole thing below.
I tested it just now, it works fine.
Can I create a v3 patch based your patch? or you do it yourself.
Thanks
Huang Shijie
>
> Thanks,
>
> M.
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 93c541111dea..fb875c5c0347 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -49,6 +49,7 @@
> #define KVM_REQ_RELOAD_GICv4 KVM_ARCH_REQ(4)
> #define KVM_REQ_RELOAD_PMU KVM_ARCH_REQ(5)
> #define KVM_REQ_SUSPEND KVM_ARCH_REQ(6)
> +#define KVM_REQ_RELOAD_GUEST_PMU_EVENTS KVM_ARCH_REQ(7)
>
> #define KVM_DIRTY_LOG_MANUAL_CAPS (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE | \
> KVM_DIRTY_LOG_INITIALLY_SET)
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 8b51570a76f8..b40db24f1f0b 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -804,6 +804,9 @@ static int check_vcpu_requests(struct kvm_vcpu *vcpu)
> kvm_pmu_handle_pmcr(vcpu,
> __vcpu_sys_reg(vcpu, PMCR_EL0));
>
> + if (kvm_check_request(KVM_REQ_RELOAD_GUEST_PMU_EVENTS, vcpu))
> + kvm_vcpu_pmu_restore_guest(vcpu);
> +
> if (kvm_check_request(KVM_REQ_SUSPEND, vcpu))
> return kvm_vcpu_suspend(vcpu);
>
> diff --git a/arch/arm64/kvm/pmu.c b/arch/arm64/kvm/pmu.c
> index 121f1a14c829..7bd1facc8f15 100644
> --- a/arch/arm64/kvm/pmu.c
> +++ b/arch/arm64/kvm/pmu.c
> @@ -236,3 +236,17 @@ bool kvm_set_pmuserenr(u64 val)
> ctxt_sys_reg(hctxt, PMUSERENR_EL0) = val;
> return true;
> }
> +
> +void kvm_resync_guest_context(void)
> +{
> + struct kvm_vcpu *vcpu;
> +
> + if (!kvm_arm_support_pmu_v3() || !has_vhe())
> + return;
> +
> + vcpu = kvm_get_running_vcpu();
> + if (!vcpu)
> + return;
> +
> + kvm_make_request(KVM_REQ_RELOAD_GUEST_PMU_EVENTS, vcpu);
> +}
> diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c
> index 08b3a1bf0ef6..7012de417092 100644
> --- a/drivers/perf/arm_pmuv3.c
> +++ b/drivers/perf/arm_pmuv3.c
> @@ -772,6 +772,9 @@ static void armv8pmu_start(struct arm_pmu *cpu_pmu)
>
> /* Enable all counters */
> armv8pmu_pmcr_write(armv8pmu_pmcr_read() | ARMV8_PMU_PMCR_E);
> +
> + if (in_interrupt())
> + kvm_resync_guest_context();
> }
>
> static void armv8pmu_stop(struct arm_pmu *cpu_pmu)
> diff --git a/include/kvm/arm_pmu.h b/include/kvm/arm_pmu.h
> index 847da6fc2713..d66f7216b5a9 100644
> --- a/include/kvm/arm_pmu.h
> +++ b/include/kvm/arm_pmu.h
> @@ -74,6 +74,7 @@ int kvm_arm_pmu_v3_enable(struct kvm_vcpu *vcpu);
> struct kvm_pmu_events *kvm_get_pmu_events(void);
> void kvm_vcpu_pmu_restore_guest(struct kvm_vcpu *vcpu);
> void kvm_vcpu_pmu_restore_host(struct kvm_vcpu *vcpu);
> +void kvm_resync_guest_context(void);
>
> #define kvm_vcpu_has_pmu(vcpu) \
> (test_bit(KVM_ARM_VCPU_PMU_V3, (vcpu)->arch.features))
> @@ -171,6 +172,7 @@ static inline u8 kvm_arm_pmu_get_pmuver_limit(void)
> {
> return 0;
> }
> +static inline void kvm_resync_guest_context(void) {}
>
> #endif
>
>
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