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Re: [PATCH for-6.1 v2] machine: Disallow specifying topology parameters
From: |
Markus Armbruster |
Subject: |
Re: [PATCH for-6.1 v2] machine: Disallow specifying topology parameters as zero |
Date: |
Fri, 23 Jul 2021 10:02:43 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) |
Daniel P. Berrangé <berrange@redhat.com> writes:
> On Thu, Jul 22, 2021 at 11:43:26PM +0800, Yanan Wang wrote:
>> In the SMP configuration, we should either specify a topology
>> parameter with a reasonable value (equal to or greater than 1)
>> or just leave it omitted and QEMU will calculate its value.
>> Configurations which explicitly specify the topology parameters
>> as zero like "sockets=0" are meaningless, so disallow them.
>>
>> However, the commit 1e63fe685804d
>> (machine: pass QAPI struct to mc->smp_parse) has documented that
>> '0' has the same semantics as omitting a parameter in the qapi
>> comment for SMPConfiguration. So this patch fixes the doc and
>> also adds the corresponding sanity check in the smp parsers.
>>
>> Suggested-by: Andrew Jones <drjones@redhat.com>
>> Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
>> ---
>> hw/core/machine.c | 14 ++++++++++++++
>> qapi/machine.json | 6 +++---
>> qemu-options.hx | 12 +++++++-----
>> 3 files changed, 24 insertions(+), 8 deletions(-)
>>
>> diff --git a/hw/core/machine.c b/hw/core/machine.c
>> index 775add0795..db129d937b 100644
>> --- a/hw/core/machine.c
>> +++ b/hw/core/machine.c
>> @@ -829,6 +829,20 @@ static void machine_set_smp(Object *obj, Visitor *v,
>> const char *name,
>> return;
>> }
>>
>> + /*
>> + * The topology parameters must be specified equal to or great than one
>> + * or just omitted, explicit configuration like "cpus=0" is not allowed.
>> + */
>> + if ((config->has_cpus && config->cpus == 0) ||
>> + (config->has_sockets && config->sockets == 0) ||
>> + (config->has_dies && config->dies == 0) ||
>> + (config->has_cores && config->cores == 0) ||
>> + (config->has_threads && config->threads == 0) ||
>> + (config->has_maxcpus && config->maxcpus == 0)) {
>> + error_setg(errp, "parameters must be equal to or greater than one
>> if provided");
>
> I'd suggest a slight tweak since when seen it lacks context:
>
> $ ./qemu-system-x86_64 -smp 4,cores=0,sockets=2
> qemu-system-x86_64: parameters must be equal to or greater than one if
> provided
>
>
> error_setg(errp, "CPU topology parameters must be equal to or greater
> than one if provided");
Let's scratch "if provided".
I'd replace "must be equal to or greater than one" by "must be
positive", or maybe "must be greater than zero".
>> diff --git a/qemu-options.hx b/qemu-options.hx
>> index 99ed5ec5f1..b0168f8c48 100644
>> --- a/qemu-options.hx
>> +++ b/qemu-options.hx
>> @@ -223,11 +223,13 @@ SRST
>> of computing the CPU maximum count.
>>
>> Either the initial CPU count, or at least one of the topology parameters
>> - must be specified. Values for any omitted parameters will be computed
>> - from those which are given. Historically preference was given to the
>> - coarsest topology parameters when computing missing values (ie sockets
>> - preferred over cores, which were preferred over threads), however, this
>> - behaviour is considered liable to change.
>> + must be specified. The specified parameters must be equal to or great
>
> s/great/greater/
>
>> + than one, explicit configuration like "cpus=0" is not allowed. Values
"positive" again.
>> + for any omitted parameters will be computed from those which are given.
>> + Historically preference was given to the coarsest topology parameters
>> + when computing missing values (ie sockets preferred over cores, which
>> + were preferred over threads), however, this behaviour is considered
>> + liable to change.
>> ERST
>
>
> If you make the text changes, then feel free to add this when posting v2:
>
> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
> Tested-by: Daniel P. Berrangé <berrange@redhat.com>
>
>
>
> Regards,
> Daniel