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Date: Tue, 18 May 2021 06:52:22 +0000
From: Salil Mehta <salil.mehta@...wei.com>
To: "wangyanan (Y)" <wangyanan55@...wei.com>
CC: Peter Maydell <peter.maydell@...aro.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Andrew Jones <drjones@...hat.com>,
"Michael S . Tsirkin" <mst@...hat.com>,
Igor Mammedov <imammedo@...hat.com>,
Shannon Zhao <shannon.zhaosl@...il.com>,
"qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
"qemu-arm@...gnu.org" <qemu-arm@...gnu.org>,
Philippe Mathieu-Daudé <philmd@...hat.com>,
yangyicong <yangyicong@...wei.com>,
"Zengtao (B)" <prime.zeng@...ilicon.com>,
"Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>,
"Wanghaibin (D)" <wanghaibin.wang@...wei.com>,
zhukeqian <zhukeqian1@...wei.com>,
yuzenghui <yuzenghui@...wei.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linuxarm@...neuler.org" <linuxarm@...neuler.org>
Subject: RE: [RFC PATCH v3 4/4] hw/arm/virt: Parse -smp cluster parameter in
virt_smp_parse
> From: wangyanan (Y)
>
> Hi Salil,
>
> On 2021/5/17 23:17, Salil Mehta wrote:
> >> From: Qemu-devel
> >> [mailto:qemu-devel-bounces+salil.mehta=huawei.com@...gnu.org] On Behalf Of
> >> Yanan Wang
> >> Sent: Sunday, May 16, 2021 11:32 AM
> >> To: Peter Maydell <peter.maydell@...aro.org>; Paolo Bonzini
> >> <pbonzini@...hat.com>; Andrew Jones <drjones@...hat.com>; Michael S . Tsirkin
> >> <mst@...hat.com>; Igor Mammedov <imammedo@...hat.com>; Shannon Zhao
> >> <shannon.zhaosl@...il.com>; qemu-devel@...gnu.org; qemu-arm@...gnu.org
> >> Cc: Song Bao Hua (Barry Song) <song.bao.hua@...ilicon.com>; Philippe
> >> Mathieu-Daudé <philmd@...hat.com>; wangyanan (Y) <wangyanan55@...wei.com>;
> >> Zengtao (B) <prime.zeng@...ilicon.com>; Wanghaibin (D)
> >> <wanghaibin.wang@...wei.com>; yuzenghui <yuzenghui@...wei.com>; yangyicong
> >> <yangyicong@...wei.com>; zhukeqian <zhukeqian1@...wei.com>
> >> Subject: [RFC PATCH v3 4/4] hw/arm/virt: Parse -smp cluster parameter in
> >> virt_smp_parse
> >>
> >> There is a separate function virt_smp_parse() in hw/virt/arm.c used
> >> to parse cpu topology for the ARM machines. So add parsing of -smp
> >> cluster parameter in it, then total number of logical cpus will be
> >> calculated like: max_cpus = sockets * clusters * cores * threads.
> >>
> >> Note, we will assume multi-cluster in one socket is not supported
> >> and default the value of clusters to 1, if it's not explicitly
> >> specified in -smp cmdline.
> >>
> >> Signed-off-by: Yanan Wang <wangyanan55@...wei.com>
> >> ---
> >> hw/arm/virt.c | 32 ++++++++++++++++++--------------
> >> 1 file changed, 18 insertions(+), 14 deletions(-)
> >>
> >> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> >> index 7de822e491..678d5ef36c 100644
> >> --- a/hw/arm/virt.c
> >> +++ b/hw/arm/virt.c
> >> @@ -2642,8 +2642,8 @@ static int virt_kvm_type(MachineState *ms, const char
> >> *type_str)
> >> * with the -smp cmdlines when parsing them.
> >> *
> >> * We require that at least one of cpus or maxcpus must be provided.
> >> - * Threads will default to 1 if not provided. Sockets and cores must
> >> - * be either both provided or both not.
> >> + * Clusters and threads will default to 1 if they are not provided.
> >> + * Sockets and cores must be either both provided or both not.
> >> *
> >> * Note, if neither sockets nor cores are specified, we will calculate
> >> * all the missing values just like smp_parse() does, but will disable
> >> @@ -2652,15 +2652,18 @@ static int virt_kvm_type(MachineState *ms, const char
> >> *type_str)
> >> static void virt_smp_parse(MachineState *ms, QemuOpts *opts)
> >> {
> >> VirtMachineClass *vmc = VIRT_MACHINE_GET_CLASS(ms);
> >> + VirtMachineState *vms = VIRT_MACHINE(ms);
> >>
> >> if (opts) {
> >> unsigned cpus = qemu_opt_get_number(opts, "cpus", 0);
> >> unsigned maxcpus = qemu_opt_get_number(opts, "maxcpus", 0);
> >> unsigned sockets = qemu_opt_get_number(opts, "sockets", 0);
> >> + unsigned clusters = qemu_opt_get_number(opts, "clusters", 0);
> >> unsigned cores = qemu_opt_get_number(opts, "cores", 0);
> >> unsigned threads = qemu_opt_get_number(opts, "threads", 0);
> >>
> >> - /* Default threads to 1 if not provided */
> >> + /* Default clusters and threads to 1 if not provided */
> >> + clusters = clusters > 0 ? clusters : 1;
> >> threads = threads > 0 ? threads : 1;
> >>
> >> if (cpus == 0 && maxcpus == 0) {
> >> @@ -2676,13 +2679,13 @@ static void virt_smp_parse(MachineState *ms, QemuOpts
> >> *opts)
> >> cores = 1;
> >> if (cpus == 0) {
> >> sockets = 1;
> >> - cpus = sockets * cores * threads;
> >> + cpus = sockets * clusters * cores * threads;
> >> } else {
> >> maxcpus = maxcpus > 0 ? maxcpus : cpus;
> >> - sockets = maxcpus / (cores * threads);
> >> + sockets = maxcpus / (clusters * cores * threads);
> >> }
> >> } else if (sockets > 0 && cores > 0) {
> >> - cpus = cpus > 0 ? cpus : sockets * cores * threads;
> >> + cpus = cpus > 0 ? cpus : sockets * clusters * cores * threads;
> >> maxcpus = maxcpus > 0 ? maxcpus : cpus;
> >> } else {
> >> error_report("sockets and cores must be both provided "
> >> @@ -2695,25 +2698,26 @@ static void virt_smp_parse(MachineState *ms, QemuOpts
> >> *opts)
> >> exit(1);
> >> }
> >>
> >> - if (sockets * cores * threads < cpus) {
> >> + if (sockets * clusters * cores * threads < cpus) {
> >> error_report("cpu topology: "
> >> - "sockets (%u) * cores (%u) * threads (%u) < "
> >> - "smp_cpus (%u)",
> >> - sockets, cores, threads, cpus);
> >> + "sockets (%u) * clusters (%u) * cores (%u) * "
> >> + "threads (%u) < smp_cpus (%u)",
> >> + sockets, clusters, cores, threads, cpus);
> >> exit(1);
> >> }
> >>
> >> - if (sockets * cores * threads != maxcpus) {
> >> + if (sockets * clusters * cores * threads != maxcpus) {
> >> error_report("cpu topology: "
> >> - "sockets (%u) * cores (%u) * threads (%u) "
> >> - "!= maxcpus (%u)",
> >> - sockets, cores, threads, maxcpus);
> >> + "sockets (%u) * clusters (%u) * cores (%u) * "
> >> + "threads (%u) != maxcpus (%u)",
> >> + sockets, clusters, cores, threads, maxcpus);
> >> exit(1);
> >> }
> >>
> >> ms->smp.cpus = cpus;
> >> ms->smp.max_cpus = maxcpus;
> >> ms->smp.sockets = sockets;
> >> + vms->smp_clusters = clusters;
> >
> > This variable naming *smp_clusters* looks out-of-sorts. I thought a similar
> > variable *smp_cpus* was destined to be removed for the reason given in below
> > link - a patch by Andrew Jones?
> >
> > Link: https://lists.gnu.org/archive/html/qemu-arm/2020-12/msg00418.html
> >
> > Am I missing anything here?
> The smp_clusters is added in VirtMachineState and nowhere else because
> it's currently only used for ARM. But I think maybe I should also move it to
> CpuTopology structure like [1] is doing to move dies to CpuTopology.
yes, that’s the idea. It is always good to have right place holders so that
the code comprehension/usage(in this case) becomes easy and obvious.
>
> Move clusters to CpuTopology won't affect other architectures that don't
> support it yet, and will also make it easy if they want to in the future.
>
> [1] From Paolo:
> https://patchwork.kernel.org/project/qemu-devel/patch/20210513162901.131023
> 9-10-pbonzini@...hat.com/
sure.
>
> Thanks,
> Yanan
> > Salil.
> >
> >> ms->smp.cores = cores;
> >> ms->smp.threads = threads;
> >> }
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