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[RFC,0/4] cpu: Drop CPUState::nr_cores

Message ID 20241205145716.472456-1-xiaoyao.li@intel.com (mailing list archive)
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Series cpu: Drop CPUState::nr_cores | expand

Message

Xiaoyao Li Dec. 5, 2024, 2:57 p.m. UTC 
The series is motivated by auditing the usage of CPUState::nr_cores and
CPUState::nr_threads, which is motivated by [1].

The initial goal is to initialize nr_threads and nr_cores earlier for
x86, which leads to patches [2] and [3]. Patch [2] touches all the ARCHes
and patch [3] looks hacky. At last Igor suggested to audit nr_threads and
nr_cores, and only set them in the pre_plug() callback for the ARCHes that
really need them[1].

By audting nr_threads and nr_cores, I found nr_cores is only used by
x86. So we can introduce a x86 specific one and initialize in
x86_cpu_pre_plug(), then drop nr_cores totally.

However for nr_threads, it's used by MIPS and PPC as well[4]. There are
two options:
1. maintain separate substitute in X86/MIPS/PPS, so we can drop
CPUState::nr_threads like for CPUState::nr_cores.

2. keep CPUState::nr_threads and find place (or introduce pre_plug()) to
initialize them earlier for MIPS/PPC.

I would like to seek for opinions for which one is prefered. 

This series implments the drop for CPUState::nr_cores. Though it doesn't
help on the initial goal without the solution for nr_threads, I think it
is still a good cleanup?

BTW, by initializing nr_threads and nr_cores earlier than
qemu_init_vcpu(), it also unblocks [5].


[1] https://lore.kernel.org/qemu-devel/20241125103857.78a23715@imammedo.users.ipa.redhat.com/
[2] https://lore.kernel.org/qemu-devel/5f8db586-cdda-4d00-be02-f9880a20e1a3@redhat.com/
[3] https://lore.kernel.org/qemu-devel/20241122160317.4070177-1-xiaoyao.li@intel.com/
[4] https://lore.kernel.org/qemu-devel/045f9cb1-2b17-4b2c-985f-3c34e3626b36@intel.com/
[5] https://lore.kernel.org/qemu-devel/20231128171239.69b6d7b1@imammedo.users.ipa.redhat.com/

Xiaoyao Li (4):
  i386/topology: Update the comment of x86_apicid_from_topo_ids()
  i386: Extract a common fucntion to setup value of
    MSR_CORE_THREAD_COUNT
  i386: Track cores_per_module in CPUX86State
  cpu: Remove nr_cores from struct CPUState

 hw/core/cpu-common.c                 |  1 -
 hw/i386/x86-common.c                 |  4 +++-
 include/hw/core/cpu.h                |  2 --
 include/hw/i386/topology.h           |  5 +++--
 system/cpus.c                        |  1 -
 target/i386/cpu.c                    |  2 +-
 target/i386/cpu.h                    | 16 ++++++++++++++++
 target/i386/hvf/x86_emu.c            |  3 +--
 target/i386/kvm/kvm.c                |  5 +----
 target/i386/tcg/sysemu/misc_helper.c |  3 +--
 10 files changed, 26 insertions(+), 16 deletions(-)