From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 269C3C433F5 for ; Wed, 16 Mar 2022 19:17:46 +0000 (UTC) Received: from localhost ([::1]:53016 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nUZ9U-0005Qs-Jx for qemu-devel@archiver.kernel.org; Wed, 16 Mar 2022 15:17:44 -0400 Received: from eggs.gnu.org ([209.51.188.92]:44592) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nUZ8Y-0004bE-QW for qemu-devel@nongnu.org; Wed, 16 Mar 2022 15:16:46 -0400 Received: from 8.mo552.mail-out.ovh.net ([46.105.37.156]:57439) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nUZ8W-00047N-BW for qemu-devel@nongnu.org; Wed, 16 Mar 2022 15:16:46 -0400 Received: from mxplan5.mail.ovh.net (unknown [10.108.20.235]) by mo552.mail-out.ovh.net (Postfix) with ESMTPS id 6E4CE2979B; Wed, 16 Mar 2022 19:16:40 +0000 (UTC) Received: from kaod.org (37.59.142.107) by DAG4EX1.mxp5.local (172.16.2.31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Wed, 16 Mar 2022 20:16:39 +0100 Authentication-Results: garm.ovh; auth=pass (GARM-107S001b7b8b53b-d952-4edd-b2e8-aa4a08cd81ce, C2F6808E47F1CA0F000971F70C7D0E7BD6BD5175) smtp.auth=clg@kaod.org X-OVh-ClientIp: 82.64.250.170 Message-ID: <6f0a92ca-9f53-b8b8-e85d-43f4da36200d@kaod.org> Date: Wed, 16 Mar 2022 20:16:39 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.2 Subject: Re: XIVE VFIO kernel resample failure in INTx mode under heavy load Content-Language: en-US From: =?UTF-8?Q?C=c3=a9dric_Le_Goater?= To: 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> In-Reply-To: <9638ec8f-2edf-97df-0c14-95ae2344dc70@kaod.org> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [37.59.142.107] X-ClientProxiedBy: DAG2EX1.mxp5.local (172.16.2.11) To DAG4EX1.mxp5.local (172.16.2.31) X-Ovh-Tracer-GUID: d5c72a47-c6a1-4cab-bed0-823bfa1a1ec5 X-Ovh-Tracer-Id: 4005951869258337187 X-VR-SPAMSTATE: OK X-VR-SPAMSCORE: -100 X-VR-SPAMCAUSE: gggruggvucftvghtrhhoucdtuddrgedvvddrudefvddguddvtdcutefuodetggdotefrodftvfcurfhrohhfihhlvgemucfqggfjpdevjffgvefmvefgnecuuegrihhlohhuthemucehtddtnecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenucfjughrpefkffggfgfuhffvfhgjtgfgihesthekredttdefjeenucfhrhhomhepveorughrihgtpgfnvggpifhorghtvghruceotghlgheskhgrohgurdhorhhgqeenucggtffrrghtthgvrhhnpeeihfefffffgedtkeegtdekffevudeggfegffethfffhefhhfevhfdtudejhfdvieenucfkpheptddrtddrtddrtddpfeejrdehledrudegvddruddtjeenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepmhhouggvpehsmhhtphhouhhtpdhhvghlohepmhigphhlrghnhedrmhgrihhlrdhovhhhrdhnvghtpdhinhgvtheptddrtddrtddrtddpmhgrihhlfhhrohhmpegtlhhgsehkrghougdrohhrghdpnhgspghrtghpthhtohepuddprhgtphhtthhopehqvghmuhdquggvvhgvlhesnhhonhhgnhhurdhorhhg Received-SPF: pass client-ip=46.105.37.156; envelope-from=clg@kaod.org; helo=8.mo552.mail-out.ovh.net 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, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, 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: Alexey Kardashevskiy , "list@suse.de:PowerPC" , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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. Thanks, C.