Re: [FFmpeg-devel] [PATCH] checkasm: Test whether direct cycle counter access works

["Rémi Denis-Courmont" <remi@remlab.net>]

Le torstaina 11. tammikuuta 2024, 16.15.29 EET Martin Storsjö a écrit :
> > AV_READ_TIME() reads time, not cycles.
> 
> Right, I can adjust the wording. Exactly what kind of measurement
> AV_READ_TIME returns varies between architectures and environments indeed.

In practice, yes, but I would argue that it's a bug if it does not measure 
time. At the very least because, the name is extremely misleading.

> What about:
> 
>      checkasm: unable to execute platform specific timer
> 
> > If we want cycle count, then we should add a separate macro, as the two
> > are different performance counters at least on RISC-V.
> 
> That's not what I try to do here, I just want to test whether the timer,
> whatever we have in AV_READ_TIME, is usable.

Sure, I can live with that, but I thought that checkasm actually prefered to 
measure cycles than time periods.

> > As things stand, this code won't do anything on RISC-V, sinec
> > AV_READ_TIME() actually reads, well, time, not cycles.
> 
> Should I interpret this, as, the current AV_READ_TIME implementation on
> RISC-V always succeeds, contrary to the previous implementation (with
> rdcycle) which is unavailable on some systems, referencing
> 05115a77e012331b6ff5e24bab40e75848447c62?

Yes.

-- 
雷米‧德尼-库尔蒙
http://www.remlab.net/



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