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Re: [PATCH v11 11/14] machine: Make smp_parse generic enough for all arc

From: wangyanan (Y)
Subject: Re: [PATCH v11 11/14] machine: Make smp_parse generic enough for all arches
Date: Tue, 28 Sep 2021 20:53:32 +0800
User-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0

On 2021/9/28 20:25, Markus Armbruster wrote:
Philippe Mathieu-Daudé <philmd@redhat.com> writes:

On 9/28/21 05:57, Yanan Wang wrote:
Currently the only difference between smp_parse and pc_smp_parse
is the support of dies parameter and the related error reporting.
With some arch compat variables like "bool dies_supported", we can
make smp_parse generic enough for all arches and the PC specific
one can be removed.

Making smp_parse() generic enough can reduce code duplication and
ease the code maintenance, and also allows extending the topology
with more arch specific members (e.g., clusters) in the future.

Suggested-by: Andrew Jones <drjones@redhat.com>
Suggested-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
  hw/core/machine.c   | 91 +++++++++++++++++++++++++++++++++++----------
  hw/i386/pc.c        | 84 +----------------------------------------
  include/hw/boards.h |  9 +++++
  3 files changed, 81 insertions(+), 103 deletions(-)
+ * smp_parse - Generic function used to parse the given SMP configuration
+ *
+ * Any missing parameter in "cpus/maxcpus/sockets/cores/threads" will be
+ * automatically computed based on the provided ones.
+ *
+ * In the calculation of omitted sockets/cores/threads: we prefer sockets
+ * over cores over threads before 6.2, while preferring cores over sockets
+ * over threads since 6.2.
+ *
+ * In the calculation of cpus/maxcpus: When both maxcpus and cpus are omitted,
+ * maxcpus will be computed from the given parameters and cpus will be set
+ * equal to maxcpus. When only one of maxcpus and cpus is given then the
+ * omitted one will be set to its given counterpart's value. Both maxcpus and
+ * cpus may be specified, but maxcpus must be equal to or greater than cpus.
+ *
+ * For compatibility, apart from the parameters that will be computed, newly
+ * introduced topology members which are likely to be target specific should
+ * be directly set as 1 if they are omitted (e.g. dies for PC since 4.1).
+ */
  static void smp_parse(MachineState *ms, SMPConfiguration *config, Error 
Can we have it return a boolean instead?
Yes, please.  From error.h's big comment:

  * = Rules =
  * - Whenever practical, also return a value that indicates success /
  *   failure.  This can make the error checking more concise, and can
  *   avoid useless error object creation and destruction.  Note that
  *   we still have many functions returning void.  We recommend
  *   • bool-valued functions return true on success / false on failure,
  *   • pointer-valued functions return non-null / null pointer, and
  *   • integer-valued functions return non-negative / negative.
Ok. I will add an extra patch to this series to do the change and respin.
In practice the boolean return value will also make a smp parsing unit
test more concise. (I'm planning to introduce one test).


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