Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debugging for official releases

[Anthony Liguori]

Paolo Bonzini <address@hidden> writes:

> Il 10/05/2013 15:23, Andreas Färber ha scritto:
>> Am 10.05.2013 15:08, schrieb Paolo Bonzini:
>>> Il 10/05/2013 15:01, Anthony Liguori ha scritto:
>>>> I'd prefer not to disable but instead focus on improving performance.
>>>
>>> For 1.5?  This is a regression in 1.5 due to more and more usage of
>>> foo_env_on_cpu.
>> 
>> If CPUs were the only reason, we could simply change those inlines and
>> ENV_GET_CPU() macro to use a C cast. No complicated interface scenarios
>> requiring a dynamic cast are used for CPUs so far to my knowledge.
>
> Almost nothing really requires a dynamic cast in QEMU.  Only interface
> casts do, and there's just a couple of uses of interfaces.
>
> And I wrote in the cover letter that what I want is really avoid the
> need for "fast casts" in the hot paths.
>
> Can you guys actually read the commit messages?

Yeah, the vast majority of the series is a nice cleanup.

I just oppose the notion of disabling casts and *especially* only
disabling casts for official builds.

I don't see a reason to do something like this without even attempting
to improve performance first.

Regards,

Anthony Liguori

>> Either way, it would be nice to see the call sites of those
>> most-impacting dynamic casts! So far I held back my APIC RFC since I'm
>> not sure how to reproducibly profile things.
>
> It's interrupts (both sending and returning from them).
>
> Paolo