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Re: [PATCH v2 4/4] qemu-options: rewrite help for -smp options
From: |
Pankaj Gupta |
Subject: |
Re: [PATCH v2 4/4] qemu-options: rewrite help for -smp options |
Date: |
Wed, 14 Jul 2021 05:06:09 +0200 |
> The -smp option help is peculiarly specific about mentioning the CPU
> upper limits, but these are wrong. The "PC" target has varying max
> CPU counts depending on the machine type picked. Notes about guest
> OS limits are inappropriate for QEMU docs. There are way too many
> machine types for it to be practical to mention actual limits, and
> some limits are even modified by downstream distribtions. Thus it
> is better to remove the specific limits entirely.
>
> The CPU topology reporting is also not neccessarily specific to the
> PC platform and descriptions around the rules of usage are somewhat
> terse. Expand this information with some examples to show effects
> of defaulting.
>
> Reviewed-by: Andrew Jones <drjones@redhat.com>
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
> ---
> qemu-options.hx | 29 +++++++++++++++++++++--------
> 1 file changed, 21 insertions(+), 8 deletions(-)
>
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 14ff35dd4e..214c477dcc 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -207,14 +207,27 @@ DEF("smp", HAS_ARG, QEMU_OPTION_smp,
> QEMU_ARCH_ALL)
> SRST
> ``-smp
> [[cpus=]n][,maxcpus=maxcpus][,sockets=sockets][,dies=dies][,cores=cores][,threads=threads]``
> - Simulate an SMP system with n CPUs. On the PC target, up to 255 CPUs
> - are supported. On Sparc32 target, Linux limits the number of usable
> - CPUs to 4. For the PC target, the number of cores per die, the
> - number of threads per cores, the number of dies per packages and the
> - total number of sockets can be specified. Missing values will be
> - computed. If any on the three values is given, the total number of
> - CPUs n can be omitted. maxcpus specifies the maximum number of
> - hotpluggable CPUs.
> + Simulate a SMP system with '\ ``n``\ ' CPUs initially present on
> + the machine type board. On boards supporting CPU hotplug, the optional
> + '\ ``maxcpus``\ ' parameter can be set to enable further CPUs to be
> + added at runtime. If omitted the maximum number of CPUs will be
> + set to match the initial CPU count. Both parameters are subject to
> + an upper limit that is determined by the specific machine type chosen.
> +
> + To control reporting of CPU topology information, the number of sockets,
> + dies per socket, cores per die, and threads per core can be specified.
> + The sum `` sockets * cores * dies * threads `` must be equal to the
> + maximum CPU count. CPU targets may only support a subset of the topology
> + parameters. Where a CPU target does not support use of a particular
> + topology parameter, its value should be assumed to be 1 for the purpose
> + 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.
> ERST
>
> DEF("numa", HAS_ARG, QEMU_OPTION_numa,
> --
Reviewed-by: Pankaj Gupta <pankaj.gupta@ionos.com>