David Gibson <da...@gibson.dropbear.id.au> writes: > On Wed, Sep 20, 2017 at 09:50:24AM +0530, Nikunj A Dadhania wrote: >> David Gibson <da...@gibson.dropbear.id.au> writes: >> >> > On Fri, Sep 15, 2017 at 02:39:16PM +0530, Nikunj A Dadhania wrote: >> >> David Gibson <da...@gibson.dropbear.id.au> writes: >> >> >> >> > On Fri, Sep 15, 2017 at 01:53:15PM +0530, Nikunj A Dadhania wrote: >> >> >> David Gibson <da...@gibson.dropbear.id.au> writes: >> >> >> >> >> >> >> >> >> >> >> I thought, I am doing the same here for PowerNV, number of online >> >> >> >> cores >> >> >> >> is equal to initial online vcpus / threads per core >> >> >> >> >> >> >> >> int boot_cores_nr = smp_cpus / smp_threads; >> >> >> >> >> >> >> >> Only difference that I see in PowerNV is that we have multiple chips >> >> >> >> (max 2, at the moment) >> >> >> >> >> >> >> >> cores_per_chip = smp_cpus / (smp_threads * pnv->num_chips); >> >> >> > >> >> >> > This doesn't make sense to me. Cores per chip should *always* equal >> >> >> > smp_cores, you shouldn't need another calculation for it. >> >> >> > >> >> >> >> And in case user has provided sane smp_cores, we use it. >> >> >> > >> >> >> > If smp_cores isn't sane, you should simply reject it, not try to fix >> >> >> > it. That's just asking for confusion. >> >> >> >> >> >> This is the case where the user does not provide a topology(which is a >> >> >> valid scenario), not sure we should reject it. So qemu defaults >> >> >> smp_cores/smt_threads to 1. I think it makes sense to over-ride. >> >> > >> >> > If you can find a way to override it by altering smp_cores when it's >> >> > not explicitly specified, then ok. >> >> >> >> Should I change the global smp_cores here as well ? >> > >> > I'm pretty uneasy with that option. >> >> Me too. >> >> > It would take a fair bit of checking to ensure that changing smp_cores >> > is safe here. An easier to verify option would be to make the generic >> > logic which splits up an unspecified -smp N into cores and sockets >> > more flexible, possibly based on machine options for max values. >> > >> > That might still be more trouble than its worth. >> >> I think the current approach is the simplest and less intrusive, as we >> are handling a case where user has not bothered to provide a detailed >> topology, the best we can do is create single threaded cores equal to >> number of cores. > > No, sorry. Having smp_cores not correspond to the number of cores per > chip in all cases is just not ok. Add an error message if the > topology isn't workable for powernv by all means. But users having to > use a longer command line is better than breaking basic assumptions > about what numbers reflect what topology.
Sorry to ask again, as I am still not convinced, we do similar adjustment in spapr where the user did not provide the number of cores, but qemu assumes them as single threaded cores and created cores(boot_cores_nr) that were not same as smp_cores ? Regards Nikunj
