From: Andrew Jones <drjones@redhat.com>
To: Salil Mehta <salil.mehta@huawei.com>
Cc: Peter Maydell <peter.maydell@linaro.org>,
"linuxarm@openeuler.org" <linuxarm@openeuler.org>,
"Michael S . Tsirkin" <mst@redhat.com>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
Linuxarm <linuxarm@huawei.com>,
"wangyanan \(Y\)" <wangyanan55@huawei.com>,
Shannon Zhao <shannon.zhaosl@gmail.com>,
Igor Mammedov <imammedo@redhat.com>,
"qemu-arm@nongnu.org" <qemu-arm@nongnu.org>,
Alistair Francis <alistair.francis@wdc.com>,
"Zengtao \(B\)" <prime.zeng@hisilicon.com>,
yangyicong <yangyicong@huawei.com>,
yuzenghui <yuzenghui@huawei.com>,
"Wanghaibin \(D\)" <wanghaibin.wang@huawei.com>,
zhukeqian <zhukeqian1@huawei.com>,
"lijiajie \(H\)" <lijiajie11@huawei.com>,
David Gibson <david@gibson.dropbear.id.au>
Subject: Re: [RFC PATCH v2 5/6] hw/arm/virt-acpi-build: Add PPTT table
Date: Tue, 18 May 2021 21:05:39 +0200 [thread overview]
Message-ID: <20210518190539.fwsvl2ijb4jlzbyi@gator.home> (raw)
In-Reply-To: <80dca9f16c5b4bef9900f6cf76c99500@huawei.com>
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
>
> >
> > 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. :)
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?
Thanks,
drew
next prev parent reply other threads:[~2021-05-18 19:14 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-13 8:07 [RFC PATCH v2 0/6] hw/arm/virt: Introduce cpu topology support Yanan Wang
2021-04-13 8:07 ` [RFC PATCH v2 1/6] device_tree: Add qemu_fdt_add_path Yanan Wang
2021-04-16 4:52 ` David Gibson
2021-04-17 2:36 ` wangyanan (Y)
2021-04-19 1:13 ` David Gibson
2021-04-19 7:02 ` wangyanan (Y)
2021-04-13 8:07 ` [RFC PATCH v2 2/6] hw/arm/virt: DT: Add cpu-map Yanan Wang
2021-04-27 9:47 ` Philippe Mathieu-Daudé
2021-04-27 10:04 ` Andrew Jones
2021-04-27 12:36 ` Philippe Mathieu-Daudé
2021-04-28 6:36 ` wangyanan (Y)
2021-05-13 6:58 ` Andrew Jones
2021-05-13 7:15 ` wangyanan (Y)
2021-04-13 8:07 ` [RFC PATCH v2 3/6] hw/arm/virt-acpi-build: Distinguish possible and present cpus Yanan Wang
2021-04-27 13:18 ` Andrew Jones
2021-04-28 6:42 ` wangyanan (Y)
2021-04-27 14:50 ` Andrew Jones
2021-04-28 6:47 ` wangyanan (Y)
2021-04-13 8:07 ` [RFC PATCH v2 4/6] hw/acpi/aml-build: Add processor hierarchy node structure Yanan Wang
2021-04-27 13:37 ` Andrew Jones
2021-04-28 6:59 ` wangyanan (Y)
2021-04-13 8:07 ` [RFC PATCH v2 5/6] hw/arm/virt-acpi-build: Add PPTT table Yanan Wang
2021-04-27 14:16 ` Andrew Jones
2021-04-28 7:30 ` wangyanan (Y)
2021-05-13 5:10 ` wangyanan (Y)
2021-05-13 6:55 ` Andrew Jones
2021-05-18 7:17 ` Salil Mehta
2021-05-18 7:42 ` Andrew Jones
2021-05-18 18:34 ` Salil Mehta
2021-05-18 19:05 ` Andrew Jones [this message]
2021-05-18 19:22 ` Salil Mehta
2021-05-19 3:18 ` wangyanan (Y)
2021-05-19 7:54 ` Salil Mehta
2021-05-19 8:15 ` Andrew Jones
2021-05-19 8:42 ` wangyanan (Y)
2021-05-19 10:00 ` Salil Mehta
2021-05-19 8:27 ` Andrew Jones
2021-05-19 13:26 ` wangyanan (Y)
2021-05-19 13:40 ` wangyanan (Y)
2021-05-18 9:16 ` wangyanan (Y)
2021-04-13 8:07 ` [RFC PATCH v2 6/6] hw/arm/virt: Replace smp_parse with one that prefers cores Yanan Wang
2021-04-27 14:58 ` Andrew Jones
2021-04-28 8:04 ` wangyanan (Y)
2021-04-28 9:36 ` wangyanan (Y)
2021-04-28 10:13 ` Andrew Jones
2021-04-29 2:21 ` wangyanan (Y)
2021-04-21 7:40 ` [RFC PATCH v2 0/6] hw/arm/virt: Introduce cpu topology support wangyanan (Y)
2021-04-21 9:31 ` wangyanan (Y)
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