Re: [PATCH V2 2/5] ara virt interface of perf to support kvm guestos statistics collection in guest os

[Avi Kivity]

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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