RE: [RFC PATCH 0/3] kvm/arm: New VMID allocator based on asid(2ndapproach)

[Shameerali Kolothum Thodi]

Hi,

> -----Original Message-----
> From: Shameerali Kolothum Thodi
> Sent: 06 May 2021 17:52
> To: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; kvmarm@xxxxxxxxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx
> Cc: maz@xxxxxxxxxx; will@xxxxxxxxxx; catalin.marinas@xxxxxxx;
> james.morse@xxxxxxx; julien.thierry.kdev@xxxxxxxxx;
> suzuki.poulose@xxxxxxx; jean-philippe@xxxxxxxxxx; Linuxarm
> <linuxarm@xxxxxxxxxx>
> Subject: [RFC PATCH 0/3] kvm/arm: New VMID allocator based on asid(2nd
> approach)
> 
> This is based on a suggestion from Will [0] to try out the asid
> based kvm vmid solution as a separate VMID allocator instead of
> the shared lib approach attempted in v4[1].
> 
> The idea is to compare both the approaches and see whether the
> shared lib solution with callbacks make sense or not.

A gentle ping on this. Please take a look and let me know.

Thanks,
Shameer

> Though we are not yet using the pinned vmids yet, patch #2 has
> code for pinned vmid support. This is just to help the comparison.
> 
> Test Setup/Results
> ----------------
> The measurement was made with maxcpus set to 8 and with the
> number of VMID limited to 4-bit. The test involves running
> concurrently 40 guests with 2 vCPUs. Each guest will then
> execute hackbench 5 times before exiting.
> 
> The performance difference between the current algo and the
> new one are(avg. of 10 runs):
>     - 1.9% less entry/exit from the guest
>     - 0.5% faster
> This is more or less comparable to v4 numbers.
> 
> For the complete series, please see,
> https://github.com/hisilicon/kernel-dev/tree/private-v5.12-rc7-vmid-2nd-rfc
> 
> and for the shared asid lib v4 solution,
> https://github.com/hisilicon/kernel-dev/tree/private-v5.12-rc7-asid-v4
> 
> As you can see there are of course code duplication with this
> approach but may be this one is more easy to maintain considering
> the complexity involved.
> 
> Please take a look and let me know your feedback.
> 
> Thanks,
> Shameer
> 
> 
> [0] https://lore.kernel.org/lkml/20210422160846.GB2214@willie-the-truck/
> [1]
> https://lore.kernel.org/lkml/20210414112312.13704-1-shameerali.kolothum.t
> hodi@xxxxxxxxxx/
> 
> Julien Grall (2):
>   arch/arm64: Introduce a capability to tell whether 16-bit VMID is
>     available
>   kvm/arm: Align the VMID allocation with the arm64 ASID one
> 
> Shameer Kolothum (1):
>   kvm/arm: Introduce a new vmid allocator for KVM
> 
>  arch/arm64/include/asm/cpucaps.h   |   3 +-
>  arch/arm64/include/asm/kvm_asm.h   |   4 +-
>  arch/arm64/include/asm/kvm_host.h  |  11 +-
>  arch/arm64/include/asm/kvm_mmu.h   |   7 +-
>  arch/arm64/kernel/cpufeature.c     |   9 +
>  arch/arm64/kvm/Makefile            |   2 +-
>  arch/arm64/kvm/arm.c               | 115 ++++--------
>  arch/arm64/kvm/hyp/nvhe/hyp-main.c |   6 +-
>  arch/arm64/kvm/hyp/nvhe/tlb.c      |  10 +-
>  arch/arm64/kvm/hyp/vhe/tlb.c       |  10 +-
>  arch/arm64/kvm/mmu.c               |   1 -
>  arch/arm64/kvm/vmid.c              | 285
> +++++++++++++++++++++++++++++
>  12 files changed, 354 insertions(+), 109 deletions(-)
>  create mode 100644 arch/arm64/kvm/vmid.c
> 
> --
> 2.17.1