lkml.org 
[lkml]   [2021]   [Apr]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v4 00/16] kvm/arm: Align the VMID allocation with the arm64 ASID one
On Wed, Apr 14, 2021 at 12:22:56PM +0100, Shameer Kolothum wrote:
> Hi,
>
> This is an attempt to revive this series originally posted by
> Julien Grall[1]. The main motive to work on this now is because
> of the requirement to have Pinned KVM VMIDs and the RFC discussion
> for the same basically suggested[2] to have a common/better vmid
> allocator for KVM which this series provides.
>
> Major Changes from v3:
>
> -Changes related to Pinned ASID support.
> -Changes to take care KPTI related bits reservation.
> -Dropped support for 32 bit KVM.
> -Rebase to 5.12-rc7
>
> Individual patches have change history for any major changes
> from v3.
>
> Tests were performed on a HiSilicon D06 platform and so far not observed
> any regressions.
>
> For ASID allocation,
>
> Avg of 10 runs(hackbench -s 512 -l 200 -g 300 -f 25 -P),
> 5.12-rc7: Time:18.8119
> 5.12-rc7+v4: Time: 18.459
>
> ~1.8% improvement.
>
> For KVM VMID,
>
> 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(ag. of 10 runs):
> - 1.9% less exit from the guest
> - 0.7% faster
>
> For complete series, please see,
> https://github.com/hisilicon/kernel-dev/tree/private-v5.12-rc7-asid-v4
>
> Please take a look and let me know your feedback.

Although I think aligning the two algorithms makes sense, I'm not completely
sold on the need to abstract all this into a library and whether the
additional indirection is justified.

It would be great to compare this approach with one where portions of the
code are duplicated into a separate VMID allocator. Have you tried that to
see what it looks like? Doesn't need to be a proper patch set, but comparing
the end result might help to evaluate the proposal here.

Will

\
 
 \ /
  Last update: 2021-04-22 18:09    [W:0.101 / U:0.784 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site