Re: [PATCH v2 kvmtool 00/10] arm64: Improve PMU support on heterogeneous systems

[Alexandru Elisei <alexandru.elisei@arm.com>]

Hi,

The KVM patches were picked up, I'm hoping they land in v5.18-rc1. I'll
send a new version of the kvmtool series when that happens. I would really
appreciate some sort of review before the next iteration.

Thanks,
Alex

On Thu, Jan 27, 2022 at 04:20:23PM +0000, Alexandru Elisei wrote:
> The series can be found at [1], and the Linux patches that this series is
> based on at [2].
> 
> The series adds support for the KVM_ARM_VCPU_PMU_V3_SET_PMU PMU attribute,
> which allows userspace to set a PMU for a VCPU. This PMU is used by KVM
> when creating perf events to emulate the guest PMU.
> 
> Without settings this attribute, the PMU used when creating events is the
> first one that successfully probed when booting, but this is unreliable as
> the probe order can change (if the order of the PMUs is changed in the DTB
> or if asynchronous driver probing is enabled on the host's command line),
> and furthermore it requires the user to have intimate knowledge of how the
> PMU was chosen in order to pin the VM on the correct physical CPUs.
> 
> With KVM_ARM_VCPU_PMU_V3_SET_PMU, the user is still expected to pin the
> VCPUs on a particular set of CPUs, but now it can be any CPUs as long as
> they share the same PMU. The set does not depend anymore on the driver
> probe order and all that is necessary for the user to know is which CPUs
> are the little core and which are the big cores, in a big.little
> configuration, which I believe is more reasonable.
> 
> Patches #1-#2 are fixes and can be taken independently of this series.
> 
> Patches #3-#6 move the PMU code to aarch64, where it belongs, because the
> PMU has never been supported on KVM for arm. This also paves the way for
> pulling in the KVM_ARM_VCPU_PMU_V3_SET_PMU attribute, which was not defined
> for KVM for arm (when KVM supported arm). This also can be merged right
> now, independently of the other patches.
> 
> Patch #7 adds the cpumask_* functions which are necessary for subsequent
> patches.
> 
> Patch #9 adds basic support for KVM_ARM_VCPU_PMU_V3_SET_PMU; the user is
> still expected to use taskset to pin the entire VM to the correct CPUs.
> 
> Patch #10 adds --vcpu-affinity command line argument to pin VCPUs to the
> correct CPUs without pinning the rest of the kvmtool threads.
> 
> Changes since v1:
> 
> * Patch #2 ("bitops.h: Include wordsize.h to provide the __WORDSIZE
>   define") is new.
> 
> * Added for_each_cpu(), cpumask_and() and cpumask_subset() functions and
>   all the cpumask_* functions are added in one patch.
> 
> * Bumped NR_CPUS fro arm64 to 4096 to match the Linux Kconfig option.
> 
> * Reworked the way kvmtool specific header files were included to use
>   quotes to clearly differentiate them from the system level headers and to
>   keep the style consistent with the current code (for example, #include
>   <linux/bitops.h> is now "linux/bitops.h").
> 
> * Patch #10 ("arm64: Add --vcpu-affinity command line argument") is new.
> 
> [1] https://gitlab.arm.com/linux-arm/kvmtool-ae/-/tree/pmu-big-little-fix-v2
> [2] https://gitlab.arm.com/linux-arm/linux-ae/-/tree/pmu-big-little-fix-v4
> 
> Alexandru Elisei (10):
>   linux/err.h: Add missing stdbool.h include
>   bitops.h: Include wordsize.h to provide the __WORDSIZE define
>   arm: Move arch specific VCPU features to the arch specific function
>   arm: Get rid of the ARM_VCPU_FEATURE_FLAGS() macro
>   arm: Make the PMUv3 emulation code arm64 specific
>   arm64: Rework set_pmu_attr()
>   Add cpumask functions
>   update_headers.sh: Sync headers with Linux v5.17-rc1 + SET_PMU
>     attribute
>   arm64: Add support for KVM_ARM_VCPU_PMU_V3_SET_PMU
>   arm64: Add --vcpu-affinity command line argument
> 
>  Makefile                                      |   6 +-
>  arm/aarch32/include/asm/kernel.h              |   8 +
>  arm/aarch32/include/kvm/kvm-cpu-arch.h        |   4 -
>  arm/aarch64/arm-cpu.c                         |   3 +-
>  arm/aarch64/include/asm/kernel.h              |   8 +
>  arm/aarch64/include/asm/kvm.h                 |   4 +
>  .../arm-common => aarch64/include/asm}/pmu.h  |   0
>  arm/aarch64/include/kvm/kvm-config-arch.h     |   5 +
>  arm/aarch64/include/kvm/kvm-cpu-arch.h        |   6 -
>  arm/aarch64/kvm-cpu.c                         |  21 ++
>  arm/aarch64/kvm.c                             |  32 +++
>  arm/aarch64/pmu.c                             | 231 ++++++++++++++++
>  arm/include/arm-common/kvm-arch.h             |   7 +
>  arm/include/arm-common/kvm-config-arch.h      |   1 +
>  arm/kvm-cpu.c                                 |  14 +-
>  arm/pmu.c                                     |  76 ------
>  include/linux/bitmap.h                        |  71 +++++
>  include/linux/bitops.h                        |   4 +
>  include/linux/bits.h                          |   8 +
>  include/linux/cpumask.h                       |  67 +++++
>  include/linux/err.h                           |   2 +
>  include/linux/find.h                          |  30 ++
>  include/linux/kernel.h                        |   6 +
>  include/linux/kvm.h                           |  16 ++
>  mips/include/asm/kernel.h                     |   8 +
>  powerpc/include/asm/kernel.h                  |   8 +
>  util/bitmap.c                                 | 256 ++++++++++++++++++
>  util/find.c                                   |  40 +++
>  x86/include/asm/kernel.h                      |   8 +
>  x86/include/asm/kvm.h                         |  16 +-
>  30 files changed, 867 insertions(+), 99 deletions(-)
>  create mode 100644 arm/aarch32/include/asm/kernel.h
>  create mode 100644 arm/aarch64/include/asm/kernel.h
>  rename arm/{include/arm-common => aarch64/include/asm}/pmu.h (100%)
>  create mode 100644 arm/aarch64/pmu.c
>  delete mode 100644 arm/pmu.c
>  create mode 100644 include/linux/bitmap.h
>  create mode 100644 include/linux/bits.h
>  create mode 100644 include/linux/cpumask.h
>  create mode 100644 include/linux/find.h
>  create mode 100644 mips/include/asm/kernel.h
>  create mode 100644 powerpc/include/asm/kernel.h
>  create mode 100644 util/bitmap.c
>  create mode 100644 util/find.c
>  create mode 100644 x86/include/asm/kernel.h
> 
> -- 
> 2.31.1
> 
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