Re: [Qemu-devel] [PATCH 4/6] trace: Add per-vCPU tracing states for events with the 'vcpu' property

[Paolo Bonzini]

On 13/06/2016 14:15, Lluís Vilanova wrote:
> > That said, I am skeptical about the benefit of the interfaces you are
> > adding.  They add a lot of complication and overhead (especially
> > regarding the memory/cache overhead of the dstate array) without a clear
> > use case, in my opinion; all the processing you do at run-time is just
> > as well suited for later filtering.
> 
> This should make tracing faster on the future with multi-threaded TCG, as well
> as trace files much smaller if you're tracing something like memory
> accesses. Also, bear in mind this series was split from a much larger one for
> simplicity. The follow-up one provides much larger performance benefits by
> avoiding the generation of TCG code to call the tracing backend when a vCPU is
> not traced.

This still assumes that tracing only some VCPUs is a common use case.
Is it?...

Paolo