> From: Andrew Jones [mailto:drjo...@redhat.com] > Sent: Wednesday, May 19, 2021 9:15 AM > > On Wed, May 19, 2021 at 07:54:37AM +0000, Salil Mehta wrote: > > > From: wangyanan (Y) > > > Sent: Wednesday, May 19, 2021 4:18 AM > > > > > > > > > On 2021/5/19 3:22, Salil Mehta wrote: > > > >> From: Andrew Jones [mailto:drjo...@redhat.com] > > > >> Sent: Tuesday, May 18, 2021 8:06 PM > > > >> To: Salil Mehta <salil.me...@huawei.com> > > > >> Cc: wangyanan (Y) <wangyana...@huawei.com>; Peter Maydell > > > >> <peter.mayd...@linaro.org>; Michael S . Tsirkin <m...@redhat.com>; > > > >> Wanghaibin > > > >> (D) <wanghaibin.w...@huawei.com>; qemu-devel@nongnu.org; Shannon Zhao > > > >> <shannon.zha...@gmail.com>; qemu-...@nongnu.org; Alistair Francis > > > >> <alistair.fran...@wdc.com>; Zengtao (B) <prime.z...@hisilicon.com>; > > > >> yangyicong <yangyic...@huawei.com>; yuzenghui <yuzeng...@huawei.com>; > > > >> Igor > > > >> Mammedov <imamm...@redhat.com>; zhukeqian <zhukeqi...@huawei.com>; > > > >> lijiajie (H) > > > >> <lijiaji...@huawei.com>; David Gibson <da...@gibson.dropbear.id.au>; > > > >> Linuxarm > > > >> <linux...@huawei.com>; linux...@openeuler.org > > > >> Subject: Re: [RFC PATCH v2 5/6] hw/arm/virt-acpi-build: Add PPTT table > > > >> > > > >> On Tue, May 18, 2021 at 06:34:08PM +0000, Salil Mehta wrote: > > > >>> Those benefits, when vcpu pinning is used, are the same benefits > > > >>>> as for the host, which already use PPTT tables to describe topology, > > > >>>> even > > > >>>> though hot plug isn't supported. > > > >>> yes sure, you mean pinning vcpus according to the cpu topology for > > > >>> performance? > > > >> Yup > > > > Already Agreed :) > > > > > > > >>>> Now, if you're saying we should only generate tables for smp.cpus, > > > >>>> not > > > >>> Correct. This is what I thought we must be doing even now > > > >>> > > > >>>> smp.maxcpus, because hot plug isn't supported anyway, then I see your > > > >>>> point. But, it'd be better to require smp.cpus == smp.maxcpus in our > > > >>>> smp_parse function to do that, which we've never done before, so we > > > >>>> may > > > >>>> have trouble supporting existing command lines. > > > >>> I am trying to recall, if the vcpu Hotplug is not supported then can > > > >>> they > > > >>> ever be different? > > > >>> > > > >>> cpus = (threads * cores * sockets) > > > >>> > > > >>> static void smp_parse(MachineState *ms, QemuOpts *opts) > > > >>> { > > > >>> [...] > > > >>> > > > >>> if (sockets * cores * threads != ms->smp.max_cpus) { > > > >>> warn_report("Invalid CPU topology deprecated: " > > > >>> "sockets (%u) * cores (%u) * threads (%u) " > > > >>> "!= maxcpus (%u)", > > > >>> sockets, cores, threads, > > > >>> ms->smp.max_cpus); > > > >>> } > > > >>> [...] > > > >>> } > > > >>> > > > >>> Although, above check does not exit(1) and just warns on detecting > > > >>> invalid > > > >>> CPU topology. Not sure why? > > > >> Hmm, not sure what code you have there. I see this in > > > >> hw/core/machine.c:smp_parse > > > >> > > > >> if (ms->smp.max_cpus < cpus) { > > > >> error_report("maxcpus must be equal to or greater than > > > >> smp"); > > > >> exit(1); > > > >> } > > > >> > > > >> if (sockets * cores * threads != ms->smp.max_cpus) { > > > >> error_report("Invalid CPU topology: " > > > >> "sockets (%u) * cores (%u) * threads (%u) " > > > >> "!= maxcpus (%u)", > > > >> sockets, cores, threads, > > > >> ms->smp.max_cpus); > > > >> exit(1); > > > >> } > > > >> > > > >>> Well if you think there are subtleties to support above > > > >>> implementation and > > > >>> we cannot do it now then sure it is your call. :) > > > Hi Salil, Drew, > > > >> The problem is that -smp 4,maxcpus=8 doesn't error out today, even > > > >> though > > > >> it doesn't do anything. OTOH, -smp 4,cores=2 doesn't error out either, > > > >> but > > > >> we're proposing that it should. Maybe we can start erroring out when > > > >> cpus != maxcpus until hot plug is supported? > > > > Agreed, both don't make any sense if hotplug is not supported and > > > > ideally should > > > > fail with error. We should block any such topology configuration. > > > In the ARM-specific function virt_smp_parse() (patch 9), there already > > > have been some restrictions for the given -smp configuration. > > > We now only allow: > > > -smp N > > > -smp maxcpus=M > > > -smp N, maxcpus=M > > > > > > -smp N, sockets=X, cores=Y > > > -smp N, sockets=X, cores=Y, threads=Z > > > > > > -smp maxcpus=M, sockets=X, cores=Y > > > -smp maxcpus=M, sockets=X, cores=Y, threads=Z > > > > > > -smp N, maxcpus=M, sockets=X, cores=Y > > > -smp N, maxcpus=M, sockets=X, cores=Y, threads=Z > > > > > > and disallow the other strange and rare formats that shouldn't be > > > provided. > > > > > > It's reasonable to block the topology configuration which is not useful > > > currently. I will add the requirement for "cpus==maxcpus" in this fuction > > > if the possible conflict with existing command lines is not a big problem. > > > > Hi Yanan, > > Makes sense. I did see your other patch-set in which cluster support has > > been > > added. Are we deferring that too? > > The merge of that needs to be deferred, but for a different reason. It > shouldn't impact hot plug, because if hot plug doesn't like clusters, > then one could configure a topology which doesn't have clusters. But,
yes, agreed. > it can't be merged to QEMU until the kernel has merged its support. sure.
