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([2001:b07:6468:f312:d0d9:ea10:9775:f33f]) by smtp.gmail.com with ESMTPSA id b14sm1241888wrn.75.2020.02.28.02.36.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 28 Feb 2020 02:36:57 -0800 (PST) Subject: Re: [PATCH 0/5] vfio/pci: Fix up breakage against split irqchip and INTx To: Peter Xu , qemu-devel@nongnu.org References: <20200226225048.216508-1-peterx@redhat.com> From: Paolo Bonzini Message-ID: 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 MIME-Version: 1.0 In-Reply-To: <20200226225048.216508-1-peterx@redhat.com> Content-Language: en-US X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Eric Auger , Alex Williamson , Cornelia Huck Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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