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[110.175.254.242]) by smtp.gmail.com with ESMTPSA id g15-20020aa7818f000000b00505ce2e4640sm7866320pfi.100.2022.04.12.23.26.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 12 Apr 2022 23:26:27 -0700 (PDT) Message-ID: <560c8c1a-a87e-71f9-cfea-0a034933070b@ozlabs.ru> Date: Wed, 13 Apr 2022 16:26:23 +1000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:99.0) Gecko/20100101 Thunderbird/99.0 Subject: Re: XIVE VFIO kernel resample failure in INTx mode under heavy load Content-Language: en-US From: Alexey Kardashevskiy To: =?UTF-8?Q?C=c3=a9dric_Le_Goater?= , Alex Williamson , Timothy Pearson References: <1891893257.448156.1647023745384.JavaMail.zimbra@raptorengineeringinc.com> <20220314160952.46d5313a.alex.williamson@redhat.com> <9638ec8f-2edf-97df-0c14-95ae2344dc70@kaod.org> <6f0a92ca-9f53-b8b8-e85d-43f4da36200d@kaod.org> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2607:f8b0:4864:20::1032; envelope-from=aik@ozlabs.ru; helo=mail-pj1-x1032.google.com X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Frederic Barrat , "list@suse.de:PowerPC" , qemu-devel@nongnu.org, Nicholas Piggin , David Gibson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 4/13/22 14:56, Alexey Kardashevskiy wrote: > > > On 3/17/22 06:16, Cédric Le Goater wrote: >> Timothy, >> >> On 3/16/22 17:29, Cédric Le Goater wrote: >>> Hello, >>> >>> >>>> I've been struggling for some time with what is looking like a >>>> potential bug in QEMU/KVM on the POWER9 platform.  It appears that >>>> in XIVE mode, when the in-kernel IRQ chip is enabled, an external >>>> device that rapidly asserts IRQs via the legacy INTx level mechanism >>>> will only receive one interrupt in the KVM guest. >>> >>> Indeed. I could reproduce with a pass-through PCI adapter using >>> 'pci=nomsi'. The virtio devices operate correctly but the network >>> adapter only receives one event (*): >>> >>> >>> $ cat /proc/interrupts >>>             CPU0       CPU1       CPU2       CPU3       CPU4 >>> CPU5       CPU6       CPU7 >>>   16:       2198       1378       1519       1216          0 >>> 0          0          0  XIVE-IPI   0 Edge      IPI-0 >>>   17:          0          0          0          0       2003 >>> 1936       1335       1507  XIVE-IPI   1 Edge      IPI-1 >>>   18:          0       6401          0          0          0 >>> 0          0          0  XIVE-IRQ 4609 Level     virtio3, virtio0, >>> virtio2 >>>   19:          0          0          0          0          0 >>> 204          0          0  XIVE-IRQ 4610 Level     virtio1 >>>   20:          0          0          0          0          0 >>> 0          0          0  XIVE-IRQ 4608 Level     xhci-hcd:usb1 >>>   21:          0          1          0          0          0 >>> 0          0          0  XIVE-IRQ 4612 Level     eth1 (*) >>>   23:          0          0          0          0          0 >>> 0          0          0  XIVE-IRQ 4096 Edge      RAS_EPOW >>>   24:          0          0          0          0          0 >>> 0          0          0  XIVE-IRQ 4592 Edge      hvc_console >>>   26:          0          0          0          0          0 >>> 0          0          0  XIVE-IRQ 4097 Edge      RAS_HOTPLUG >>> >>>> Changing any one of those items appears to avoid the glitch, e.g. XICS >>> >>> XICS is very different from XIVE. The driver implements the previous >>> interrupt controller architecture (P5-P8) and the hypervisor mediates >>> the delivery to the guest. With XIVE, vCPUs are directly signaled by >>> the IC. When under KVM, we use different KVM devices for each mode : >>> >>> * KVM XIVE is a XICS-on-XIVE implementation (P9/P10 hosts) for guests >>>    not using the XIVE native interface. RHEL7 for instance. >>> * KVM XIVE native is a XIVE implementation (P9/P10 hosts) for guests >>>    using the XIVE native interface. Linux > 4.14. >>> * KVM XICS is for P8 hosts (no XIVE HW) >>> >>> VFIO adds some complexity with the source events. I think the problem >>> comes from the assertion state. I will talk about it later. >>> >>>> mode with the in-kernel IRQ chip works (all interrupts are passed >>>> through), >>> >>> All interrupts are passed through using XIVE also. Run 'info pic' in >>> the monitor. On the host, check the IRQ mapping in the debugfs file : >>> >>>    /sys/kernel/debug/powerpc/kvm-xive-* >>> >>>> and XIVE mode with the in-kernel IRQ chip disabled also works. >>> >>> In that case, no KVM device backs the QEMU device and all state >>> is in one place. >>> >>>> We >>>> are also not seeing any problems in XIVE mode with the in-kernel >>>> chip from MSI/MSI-X devices. >>> >>> Yes. pass-through devices are expected to operate correctly :) >>> >>>> The device in question is a real time card that needs to raise an >>>> interrupt every 1ms.  It works perfectly on the host, but fails in >>>> the guest -- with the in-kernel IRQ chip and XIVE enabled, it >>>> receives exactly one interrupt, at which point the host continues to >>>> see INTx+ but the guest sees INTX-, and the IRQ handler in the guest >>>> kernel is never reentered. >>> >>> ok. Same symptom as the scenario above. >>> >>>> We have also seen some very rare glitches where, over a long period >>>> of time, we can enter a similar deadlock in XICS mode. >>> >>> with the in-kernel XICS IRQ chip ? >>> >>>> Disabling >>>> the in-kernel IRQ chip in XIVE mode will also lead to the lockup >>>> with this device, since the userspace IRQ emulation cannot keep up >>>> with the rapid interrupt firing (measurements show around 100ms >>>> required for processing each interrupt in the user mode). >>> >>> MSI emulation in QEMU is slower indeed (35%). LSI is very slow because >>> it is handled as a special case in the device/driver. To maintain the >>> assertion state, all LSI handling is done with a special HCALL : >>> H_INT_ESB which is implemented in QEMU. This generates a lot of back >>> and forth in the KVM stack. >>> >>>> My understanding is the resample mechanism does some clever tricks >>>> with level IRQs, but that QEMU needs to check if the IRQ is still >>>> asserted by the device on guest EOI. >>> >>> Yes. the problem is in that area. >>> >>>> Since a failure here would >>>> explain these symptoms I'm wondering if there is a bug in either >>>> QEMU or KVM for POWER / pSeries (SPAPr) where the IRQ is not >>>> resampled and therefore not re-fired in the guest? >>> >>> KVM I would say. The assertion state is maintained in KVM for the KVM >>> XICS-on-XIVE implementation and in QEMU for the KVM XIVE native >>> device. These are good candidates. I will take a look. >> >> All works fine with KVM_CAP_IRQFD_RESAMPLE=false in QEMU. Can you please >> try this workaround for now ? I could reach 934 Mbits/sec on the passthru >> device. >> >> I clearly overlooked that part and it has been 3 years. > > > Disabling KVM_CAP_IRQFD_RESAMPLE on XIVE-capable machines seems to be > the right fix actually. > > XIVE == baremetal/vm POWER9 and newer. > XICS == baremetal/vm POWER8 and older, or VMs on any POWER (backward > compat.). > > Tested on POWER9 with a passed through XHCI host and "-append pci=nomsi" > and "-machine pseries,ic-mode=xics,kernel_irqchip=on" (and s/xics/xive/). > > When it is XIVE-on-XIVE (host and guest are XIVE), INTx is emulated in > the QEMU's H_INT_ESB handler and IRQFD_RESAMPLE is just useless in such > case (as it is designed to eliminate going to the userspace for the > EOI->INTx unmasking) and there is no pathway to call the eventfd's > irqfd_resampler_ack() from QEMU. So the VM's XHCI device receives > exactly 1 interrupt and that is it. "kernel_irqchip=off" fixes it > (obviously). > > When it is XICS-on-XIVE (host is XIVE and guest is XICS), then the VM > receives 100000 interrupts and then it gets frozen (__report_bad_irq() > is called). Which happens because (unlike XICS-on-XICS), the host XIVE's > xive_(rm|vm)_h_eoi() does not call irqfd_resampler_ack(). This fixes it: > > ============= > diff --git a/arch/powerpc/kvm/book3s_xive_template.c > b/arch/powerpc/kvm/book3s_xive_template.c > index b0015e05d99a..9f0d8e5c7f4b 100644 > --- a/arch/powerpc/kvm/book3s_xive_template.c > +++ b/arch/powerpc/kvm/book3s_xive_template.c > @@ -595,6 +595,8 @@ X_STATIC int GLUE(X_PFX,h_eoi)(struct kvm_vcpu > *vcpu, unsigned long xirr) >         xc->hw_cppr = xc->cppr; >         __x_writeb(xc->cppr, __x_tima + TM_QW1_OS + TM_CPPR); > > > +       kvm_notify_acked_irq(vcpu->kvm, 0, irq); > + >         return rc; >  } > ============= > > The host's XICS does call kvm_notify_acked_irq() (I did not test that > but the code seems to be doing so). > > After re-reading what I just wrote, I am leaning towards disabling use > of KVM_CAP_IRQFD_RESAMPLE as it seems last worked on POWER8 and never > since :) > > Did I miss something in the picture (hey Cedric)? How about disabling it like this? ===== diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c index 5bfd4aa9e5aa..c999f7b1ab1b 100644 --- a/hw/ppc/spapr_pci.c +++ b/hw/ppc/spapr_pci.c @@ -732,7 +732,7 @@ static PCIINTxRoute spapr_route_intx_pin_to_irq(void *opaque, int pin) SpaprPhbState *sphb = SPAPR_PCI_HOST_BRIDGE(opaque); PCIINTxRoute route; - route.mode = PCI_INTX_ENABLED; + route.mode = PCI_INTX_DISABLED; ===== (btw what the heck is PCI_INTX_INVERTED for?) -- Alexey