Srikar Dronamraju <sri...@linux.vnet.ibm.com> writes: > * Michael Ellerman <m...@ellerman.id.au> [2020-07-31 17:45:37]: > >> Srikar Dronamraju <sri...@linux.vnet.ibm.com> writes: >> > Currently "CACHE" domain happens to be the 2nd sched domain as per >> > powerpc_topology. This domain will collapse if cpumask of l2-cache is >> > same as SMT domain. However we could generalize this domain such that it >> > could mean either be a "CACHE" domain or a "BIGCORE" domain. >> > >> > While setting up the "CACHE" domain, check if shared_cache is already >> > set. >> >> PeterZ asked for some overview of what you're doing and why, you >> responded to his mail, but I was expecting to see that text incorporated >> here somewhere. >> > > Okay, do you want that as part of the code or documentation dir or the > changelog?
I guess a comment is best, as that's most likely to be seen by people looking at the code in future. A little bit of overview in the change log is also good. >> He also asked for some comments, which I would also like to see. >> >> >> I'm also not clear why we want to rename it to "bigcore", that's not a >> commonly understood term, I don't think it's clear to new readers what >> it means. >> >> Leaving it as the shared cache domain, and having a comment mentioning >> that "bigcores" share a cache, would be clearer I think. >> > > Today, Shared cache is equal to Big Core. However in not too distant future, > Shared cache domain and Big Core may not be the same. For example lets > assume that L2 cache were to Shrink per small core with the firmware > exposing the core as a bigcore. Then with the current design, we have a SMT > == SHARED CACHE, and a DIE. We would not have any domain at the publicised 8 > thread level. Keeping the Bigcore as a domain and mapping the shared > cache, (I am resetting the domain name as CACHE if BIGCORE==SHARED_CACHE), > helps us in this scenario. Yeah OK. In that scenario it's not really clear what the 8 thread level domain expresses, if the two "halves" of the bigcore have separate L2s. But presumably there is still some benefit to exposing it. cheers
