David Gibson <da...@gibson.dropbear.id.au> writes: > On Wed, Sep 20, 2017 at 12:48:55PM +0530, Nikunj A Dadhania wrote: >> David Gibson <da...@gibson.dropbear.id.au> writes: >> >> > On Wed, Sep 20, 2017 at 12:10:48PM +0530, Nikunj A Dadhania wrote: >> >> David Gibson <da...@gibson.dropbear.id.au> writes: >> >> >> >> > On Wed, Sep 20, 2017 at 10:43:19AM +0530, Nikunj A Dadhania wrote: >> >> >> 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 ? >> >> > >> >> > What? boot_cores_nr has absolutely nothing to do with adjusting the >> >> > topology, and it certainly doesn't assume they're single threaded. >> >> >> >> When we start a TCG guest and user provides following commandline, e.g. >> >> "-smp 4", smt_threads is set to 1 by default in vl.c. So the guest boots >> >> with 4 cores, each having 1 thread. >> > >> > Ok.. and what's the problem with that behaviour on powernv? >> >> As smp_thread defaults to 1 in vl.c, similarly smp_cores also has the >> default value of 1 in vl.c. In powernv, we were setting nr-cores like >> this: >> >> object_property_set_int(chip, smp_cores, "nr-cores", &error_fatal); >> >> Even when there were multiple cpus (-smp 4), when the guest boots up, we >> just get one core (i.e. smp_cores was 1) with single thread(smp_threads >> was 1), which is wrong as per the command-line that was provided. > > Right, so, -smp 4 defaults to 4 sockets, each with 1 core of 1 > thread. If you can't supply 4 sockets you should error, but you > shouldn't go and change the number of cores per socket.
OK, that makes sense now. And I do see that smp_cpus is 4 in the above case. Now looking more into it, i see that powernv has something called "num_chips", isnt this same as sockets ? Do we need num_chips separately? Regards, Nikunj
