Re: [PATCH 3/3] target/ppc: Increment PMC5 with inline insns

[Leandro Lupori]

On 10/25/22 16:29, Daniel Henrique Barboza wrote:

> On 10/21/22 14:01, Leandro Lupori wrote:
> > Profiling QEMU during Fedora 35 for PPC64 boot revealed that
> > 6.39% of total time was being spent in helper_insns_inc(), on a
> > POWER9 machine. To avoid calling this helper every time PMCs had
> > to be incremented, an inline implementation of PMC5 increment and
> > check for overflow was developed. This led to a reduction of
> > about 12% in Fedora's boot time.
> >
> > Signed-off-by: Leandro Lupori <leandro.lupori@eldorado.org.br>
> > ---
>
> Given that PMC5 is the counter that is most likely to be active, yeah,
> isolating the case where PMC5 is incremented standalone makes sense.
>
> Still, 12% performance gain is not too shaby. Not too shaby at all.

I've tried to move more of helper_insns_inc() to the inline 
implementation, but then performance started to decrease.

Initially I found this strange, but perf revealed a considerable 
increase of time spent in functions such as tcg_gen_code and 
liveness_pass_1.

So as this code has to be generated and optimized for most TBs, it seems 
it makes code generation slower if it's too big.

> Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>