Re: [hatari-devel] Suspicious instruction & data cache hit/miss accounting

[Eero Tamminen <oak@xxxxxxxxxxxxxx>]

Hi,

On 02/06/2018 07:20 PM, Nicolas Pomarède wrote:
> Le 06/02/2018 à 18:09, Eero Tamminen a écrit :
> > I added that statistic, but now I started to wonder about terminology,
> > what would be best understood by the users of the profiler.
> >
> > Is "prefetch" correct name for moving data from i-cache to CAHR
> > register, or do people normally interpret "prefetch" to mean reading
> > instructions from system RAM to i-cache? >
> > I.e. maybe the zero i-cache hit/miss case should be named as:
> >    "Cache holding register (CAHR) already refilled from i-cache"
> >
> > instead of my current "Already prefetched" name?
>
> In fact, I don't know if all users of the profiler are aware of these 
> low details of the CPU inner work, so finding a brief and correct 
> wording might be difficult.
>
> Most users who look for optimisations should try to increase hit values 
> and decrease miss values, ignoring this "prefetched" case (as it's 
> basically a 50% chance).

It's only visible with the cache statistics histograms command,
not in disassembly, so I think it gets pretty much ignored. :-)


> Still the motorola docs tells about CAHR in "11.2.2" :
>
> "This long word is obtained from the instruction cache o the external 
> bus in response to a prefetch request from the microsequencer."
>
> So I think that "already prefetched" is correct.
> Moving from ram to i-cache should be simply called "caching" :)

Thanks!


	- Eero