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[PATCH 0/5] vfio/pci: Fix up breakage against split irqchip and INTx
From: |
Peter Xu |
Subject: |
[PATCH 0/5] vfio/pci: Fix up breakage against split irqchip and INTx |
Date: |
Wed, 26 Feb 2020 17:50:43 -0500 |
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
- 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
I think we can consider to apply patch 1 even sooner than the rest of
the series to unbreak intx+split first.
The whole test matrix for reference:
|----------+---------+-------------------+--------------+--------------------|
| IRQ type | irqchip | TCP_STREAM (Gbps) | TCP_RR (pps) | note |
|----------+---------+-------------------+--------------+--------------------|
| msi | on | 9.39 | 17567 | |
| nomsi | on | 9.29 | 14056 | |
| msi | split | 9.36 | 17330 | |
| nomsi | split | / | / | currently broken |
| nomsi | split | 8.98 | 8977 | after patch 1 |
| nomsi | split | 9.21 | 13142 | after whole series |
|----------+---------+-------------------+--------------+--------------------|
Any review comment is welcomed. Thanks,
[1] https://bugzilla.redhat.com/show_bug.cgi?id=1786404
[2] https://patchwork.kernel.org/patch/10738541/#22609933
Peter Xu (5):
vfio/pci: Disable INTx fast path if using split irqchip
vfio/pci: Use kvm_irqchip_add_irqfd_notifier_gsi() for irqfds
KVM: Pass EventNotifier into kvm_irqchip_assign_irqfd
KVM: Kick resamplefd for split kernel irqchip
Revert "vfio/pci: Disable INTx fast path if using split irqchip"
accel/kvm/kvm-all.c | 83 +++++++++++++++++++++++++++++++++++++++---
accel/kvm/trace-events | 1 +
hw/intc/ioapic.c | 11 +++++-
hw/vfio/pci.c | 37 ++++++++-----------
include/sysemu/kvm.h | 4 ++
5 files changed, 106 insertions(+), 30 deletions(-)
--
2.24.1
- [PATCH 0/5] vfio/pci: Fix up breakage against split irqchip and INTx,
Peter Xu <=