Re: [PATCH v2] KVM: SVM: use vmsave/vmload for saving/restoring additional host state

[Paolo Bonzini]

On 16/12/20 16:12, Michael Roth wrote:
> It looks like it does save us ~20-30 cycles vs. vmload, but maybe not
> enough to justify the added complexity. Additionally, since we still
> need to call vmload when we exit to userspace, it ends up being a bit
> slower for this particular workload at least. So for now I'll plan on
> sticking to vmload'ing after vmexit and moving that to the asm code
> if there are no objections.

Yeah, agreed.  BTW you can use "./x86/run x86/vmexit.flat" from 
kvm-unit-tests to check the numbers for a wide range of vmexit paths.

Paolo

> current v2 patch, sample 1
>    ioctl entry: 1204722748832
>    pre-run:     1204722749408 ( +576)
>    post-run:    1204722750784 (+1376)
>    ioctl exit:  1204722751360 ( +576)
>    total cycles:         2528
>
> current v2 patch, sample 2
>    ioctl entry: 1204722754784
>    pre-vmrun:   1204722755360 ( +576)
>    post-vmrun:  1204722756720 (+1360)
>    ioctl exit:  1204722757312 ( +592)
>    total cycles          2528
>
> wrgsbase, sample 1
>    ioctl entry: 1346624880336
>    pre-vmrun:   1346624880912 ( +576)
>    post-vmrun:  1346624882256 (+1344)
>    ioctl exit:  1346624882912 ( +656)
>    total cycles          2576
>
> wrgsbase, sample 2
>    ioctl entry: 1346624886272
>    pre-vmrun:   1346624886832 ( +560)
>    post-vmrun:  1346624888176 (+1344)
>    ioctl exit:  1346624888816 ( +640)
>    total cycles:         2544