Re: [PATCH] riscv: KVM: Remove unnecessary vcpu kick

[Andrew Jones <ajones@ventanamicro.com>]

On Tue, Feb 18, 2025 at 04:00:24PM +0800, 项文成 wrote:
> From 30dd00f6886119ecc5c39b6b88f8617a57e598fc Mon Sep 17 00:00:00 2001
> From: BillXiang <xiangwencheng@lanxincomputing.com>
> Date: Tue, 18 Feb 2025 15:45:52 +0800
> Subject: [PATCH] riscv: KVM: Remove unnecessary vcpu kick
> 
> Hello everyone,
> I'm wondering whether it's necessary to kick the virtual hart
> after writing to the vsfile of IMSIC.
> From my understanding, writing to the vsfile should directly
> forward the interrupt as MSI to the virtual hart. This means that
> an additional kick should not be necessary, as it would cause the
> vCPU to exit unnecessarily and potentially degrade performance.
> I've tested this behavior in QEMU, and it seems to work perfectly
> fine without the extra kick.
> Would appreciate any insights or confirmation on this!
> Best regards.

The above should be in a cover letter so the commit message can
be written following the guidelines of [1]

[1] Documentation/process/submitting-patches.rst

> 
> Signed-off-by: BillXiang <xiangwencheng@lanxincomputing.com>
> ---
>  arch/riscv/kvm/aia_imsic.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/arch/riscv/kvm/aia_imsic.c b/arch/riscv/kvm/aia_imsic.c
> index a8085cd8215e..29ef9c2133a9 100644
> --- a/arch/riscv/kvm/aia_imsic.c
> +++ b/arch/riscv/kvm/aia_imsic.c
> @@ -974,7 +974,6 @@ int kvm_riscv_vcpu_aia_imsic_inject(struct kvm_vcpu *vcpu,
> 
>         if (imsic->vsfile_cpu >= 0) {
>                 writel(iid, imsic->vsfile_va + IMSIC_MMIO_SETIPNUM_LE);
> -               kvm_vcpu_kick(vcpu);

We can't completely remove the kick, but we could replace it with a
kvm_vcpu_wake_up().

There's also a kick in kvm_riscv_vcpu_vstimer_expired() which could be a
kvm_vcpu_wake_up() when hideleg has IRQ_VS_TIMER set (which it currently
always does).

Thanks,
drew

>         } else {
>                 eix = &imsic->swfile->eix[iid / BITS_PER_TYPE(u64)];
>                 set_bit(iid & (BITS_PER_TYPE(u64) - 1), eix->eip);
> --
> 2.46.2
> 
> -- 
> kvm-riscv mailing list
> kvm-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/kvm-riscv

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