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SubjectRe: [PATCH V2 2/5] ara virt interface of perf to support kvm guest os statistics collection in guest os
On 06/22/2010 05:08 AM, Zhang, Yanmin wrote:
>
>> Something that is worrying is that we don't expose group information.
>> perf will multiplex the events for us, but there will be a loss in accuracy.
>>
>>
>>> #ifdef CONFIG_HAVE_HW_BREAKPOINT
>>> #include<asm/hw_breakpoint.h>
>>> #endif
>>> @@ -753,6 +752,20 @@ struct perf_event {
>>>
>>> perf_overflow_handler_t overflow_handler;
>>>
>>> + /*
>>> + * pointers used by kvm perf paravirt interface.
>>> + *
>>> + * 1) Used in host kernel and points to host_perf_shadow which
>>> + * has information about guest perf_event
>>> + */
>>> + void *host_perf_shadow;
>>>
>>>
>> Can we have real types instead of void pointers?
>>
> I just want perf generic codes have less dependency on KVM codes.
>

One way to do that and retain type safety is to have

struct perf_client {
struct perf_client_ops *ops;
...
}

The client (kvm) can do

struct kvm_perf_client {
struct perf_client pc;
// kvm specific stuff
};

the callbacks receive struct perf_client and use container_of to reach
the kvm_perf_client that contains it.

>>> + /*
>>> + * 2) Used in guest kernel and points to guest_perf_shadow which
>>> + * is used as a communication area with host kernel. Host kernel
>>> + * copies overflow data to it when an event overflows.
>>> + */
>>> + void *guest_perf_shadow;
>>>
>>>
>> It's strange to see both guest and host parts in the same patch.
>> Splitting to separate patches will really help review.
>>
> It's a little hard to split the patches if they change the same file. Perhaps
> I could add more statements before the patch when I send it out.
>

With git, it's easy (once you're used to it):

# go back one commit:
git reset HEAD^
# selectively add bits:
git add -p
# commit first patch
git commit -s
# selectively add bits:
git add -p
# commit second patch
git commit -s


>>> @@ -1626,9 +1629,22 @@ void perf_event_task_tick(struct task_st
>>> if (ctx&& ctx->nr_events&& ctx->nr_events != ctx->nr_active)
>>> rotate = 1;
>>>
>>> - perf_ctx_adjust_freq(&cpuctx->ctx);
>>> - if (ctx)
>>> - perf_ctx_adjust_freq(ctx);
>>> +#ifdef CONFIG_KVM_PERF
>>> + if (kvm_para_available()) {
>>> + /*
>>> + * perf_ctx_adjust_freq causes lots of pmu->read which would
>>> + * trigger too many vmexit to host kernel. We disable it
>>> + * under para virt situation
>>> + */
>>> + adjust_freq = 0;
>>> + }
>>> +#endif
>>>
>>>
>> Perhaps we can have a batch read interface which will read many counters
>> at once.
>>
> It's a good idea. But that will touch many perf generic codes which causes it's hard
> to maintain or follow future changes.
>

I'm talking about the guest/host interface. So you have one vmexit and
many host perf calls.

--
error compiling committee.c: too many arguments to function



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