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Re: [PATCH 0/5] vfio/pci: Fix up breakage against split irqchip and INTx
From: |
Paolo Bonzini |
Subject: |
Re: [PATCH 0/5] vfio/pci: Fix up breakage against split irqchip and INTx |
Date: |
Fri, 28 Feb 2020 11:36:55 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 |
On 26/02/20 23:50, Peter Xu wrote:
> VFIO INTx is not working with split irqchip. On new kernels KVM_IRQFD
> will directly fail with resamplefd attached so QEMU will automatically
> fallback to the INTx slow path. However on old kernels it's still
> broken.
>
> Only until recently I noticed that this could also break PXE boot for
> assigned NICs [1]. My wild guess is that the PXE ROM will be mostly
> using INTx as well, which means we can't bypass that even if we
> enables MSI for the guest kernel.
>
> This series tries to first fix this issue function-wise, then speed up
> for the INTx again with resamplefd (mostly following the ideas
> proposed by Paolo one year ago [2]). My TCP_RR test shows that:
>
> - Before this series: this is broken, no number to show
>
> - After patch 1 (enable slow path): get 63% perf comparing to full
> kernel irqchip
Oh, I thought something like patch 1 had already been applied.
One comment: because you're bypassing IOAPIC when raising the irq, the
IOAPIC's remote_irr for example will not be set. Most OSes probably
don't care, but it's at least worth a comment.
Paolo
> - After whole series (enable fast path partly, irq injection will be
> the same as fast path, however userspace needs to intercept for
> EOI broadcast to resamplefd, though should still be faster than
> the MMIO trick for intx eoi): get 93% perf comparing to full
> kernel irqchip, which is a 46% performance boost
- Re: [PATCH v1.1 4/5] KVM: Kick resamplefd for split kernel irqchip, (continued)
Re: [PATCH 4/5] KVM: Kick resamplefd for split kernel irqchip, Paolo Bonzini, 2020/02/28
[PATCH 5/5] Revert "vfio/pci: Disable INTx fast path if using split irqchip", Peter Xu, 2020/02/26
Re: [PATCH 0/5] vfio/pci: Fix up breakage against split irqchip and INTx, Auger Eric, 2020/02/27
Re: [PATCH 0/5] vfio/pci: Fix up breakage against split irqchip and INTx,
Paolo Bonzini <=