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Re: [PATCH for-6.1 v2] machine: Disallow specifying topology parameters
From: |
Daniel P . Berrangé |
Subject: |
Re: [PATCH for-6.1 v2] machine: Disallow specifying topology parameters as zero |
Date: |
Thu, 22 Jul 2021 17:01:18 +0100 |
User-agent: |
Mutt/2.0.7 (2021-05-04) |
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");
> 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
> + 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
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