From: Like Xu <like.xu@linux.intel.com>
To: "Daniel P. Berrangé" <berrange@redhat.com>,
"caodongli@kingsoft.com" <caodongli@kingsoft.com>
Cc: ehabkost <ehabkost@redhat.com>, mst <mst@redhat.com>,
"richard.henderson" <richard.henderson@linaro.org>,
qemu-devel <qemu-devel@nongnu.org>,
pbonzini <pbonzini@redhat.com>,
Igor Mammedov <imammedo@redhat.com>
Subject: Re: [PATCH v2] hw/i386: Expand the range of CPU topologies between smp and maxcpus
Date: Tue, 27 Apr 2021 10:13:01 +0800 [thread overview]
Message-ID: <378da49d-2d66-0d47-90cb-441a4e6f8ac7@linux.intel.com> (raw)
In-Reply-To: <YIbAYqpWBG5k8yp5@redhat.com>
On 2021/4/26 21:30, Daniel P. Berrangé wrote:
> On Mon, Apr 26, 2021 at 10:08:52AM +0800, caodongli@kingsoft.com wrote:
>> Change the criteria for the initial CPU topology and maxcpus, user can
>> have more settings
>
> Can you provide a better explanation of why this is needed. What
> valid usage scenario is blocked by the current check ?
>
> AFAICT, it partially reverts an intentional change done in several
> years ago in :
>
>
> commit bc1fb850a31468ac4976f3895f01a6d981e06d0a
> Author: Igor Mammedov <imammedo@redhat.com>
> Date: Thu Sep 13 13:06:01 2018 +0200
>
> vl.c deprecate incorrect CPUs topology
>
> -smp [cpus],sockets/cores/threads[,maxcpus] should describe topology
> so that total number of logical CPUs [sockets * cores * threads]
> would be equal to [maxcpus], however historically we didn't have
> such check in QEMU and it is possible to start VM with an invalid
> topology.
> Deprecate invalid options combination so we can make sure that
> the topology VM started with is always correct in the future.
> Users with an invalid sockets/cores/threads/maxcpus values should
> fix their CLI to make sure that
> [sockets * cores * threads] == [maxcpus]
>
>
Another helpful commit would be:
commit c4332cd1dcf2964c23893ab4c0bf8d774e42a3cf
Author: Igor Mammedov <imammedo@redhat.com>
Date: Fri Sep 11 09:32:02 2020 -0400
smp: drop support for deprecated (invalid topologies)
it's was deprecated since 3.1
Support for invalid topologies is removed, the user must ensure
that topologies described with -smp include all possible cpus,
i.e. (sockets * cores * threads) == maxcpus or QEMU will
exit with error.
So is the following statement correct:
When we explicitly set the topology, we must ensure that the combination
(sockets/dies/cores/threads/maxcpus) is always valid. If we need hot plug
testing, we can only use something like "-smp 1,maxcpus = 4" since 3.1.
?
>
>>
>> Signed-off-by: Dongli Cao <caodongli@kingsoft.com>
>> ---
>> hw/i386/pc.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
>> index 8a84b25..ef2e819 100644
>> --- a/hw/i386/pc.c
>> +++ b/hw/i386/pc.c
>> @@ -751,7 +751,7 @@ void pc_smp_parse(MachineState *ms, QemuOpts *opts)
>> exit(1);
>> }
>>
>> - if (sockets * dies * cores * threads != ms->smp.max_cpus) {
>> + if (sockets * dies * cores * threads > ms->smp.max_cpus) {
>> error_report("Invalid CPU topology deprecated: "
>> "sockets (%u) * dies (%u) * cores (%u) * threads (%u) "
>> "!= maxcpus (%u)",
>
> This is
>
>> --
>> 1.8.3.1
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> caodongli@kingsoft.com
>>
>>
>
> Regards,
> Daniel
>
next prev parent reply other threads:[~2021-04-27 2:14 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-26 2:08 [PATCH v2] hw/i386: Expand the range of CPU topologies between smp and maxcpus caodongli
2021-04-26 13:30 ` Daniel P. Berrangé
2021-04-27 2:13 ` Like Xu [this message]
2021-04-27 8:34 ` Daniel P. Berrangé
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