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 X-Spam-Level: X-Spam-Status: No, score=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0BDCDC433E1 for ; Thu, 16 Jul 2020 08:06:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D831120657 for ; Thu, 16 Jul 2020 08:06:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Sj9yk514" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726232AbgGPIGr (ORCPT ); Thu, 16 Jul 2020 04:06:47 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:45895 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725921AbgGPIGq (ORCPT ); Thu, 16 Jul 2020 04:06:46 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1594886804; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=d5dhBqOnsrkp+ck3vhLEOg3slEAzg8AwB2Xf50MijXU=; b=Sj9yk514UYvUH68EtAKh9pU+JzfYul1Y4Tm6B3imaoulqNX5RQ4Sa/hIRjQ5iqugWetn7a owJAC0d+Sze/PCG8/WlBWnvRr5lkPsWuMwJw1BKWYD04/UHvi5KhnnTAOKGDlBkSWrDGLz N8MYW1KPAZHCOxSwDjmhjGXWDZhsuQk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-501-Asf4430XNjmlKVUWtpP1mw-1; Thu, 16 Jul 2020 04:06:40 -0400 X-MC-Unique: Asf4430XNjmlKVUWtpP1mw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id ECD0B800FF1; Thu, 16 Jul 2020 08:06:38 +0000 (UTC) Received: from [10.72.12.131] (ovpn-12-131.pek2.redhat.com [10.72.12.131]) by smtp.corp.redhat.com (Postfix) with ESMTP id BD9302DE69; Thu, 16 Jul 2020 08:06:25 +0000 (UTC) Subject: Re: [PATCH 0/7] *** IRQ offloading for vDPA *** To: "Michael S. Tsirkin" Cc: "Zhu, Lingshan" , alex williamson , pbonzini@redhat.com, sean.j.christopherson@intel.com, wanpengli@tencent.com, "virtualization@lists.linux-foundation.org" , "netdev@vger.kernel.org" , "kvm@vger.kernel.org" , dan daly References: <1594565524-3394-1-git-send-email-lingshan.zhu@intel.com> <70244d80-08a4-da91-3226-7bfd2019467e@redhat.com> <97032c51-3265-c94a-9ce1-f42fcc6d3075@intel.com> <77318609-85ef-f169-2a1e-500473976d84@redhat.com> <29ab6da8-ed8e-6b91-d658-f3d240543b29@intel.com> <1e91d9dd-d787-beff-2c14-9c76ffc3b285@redhat.com> <67c4c41d-9e95-2270-4acb-6f04668c34fa@redhat.com> <20200716021435-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: <918ef7c7-852e-6c0a-ed0d-fac3fa6752e4@redhat.com> Date: Thu, 16 Jul 2020 16:06:23 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200716021435-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2020/7/16 下午2:15, Michael S. Tsirkin wrote: > On Thu, Jul 16, 2020 at 12:20:09PM +0800, Jason Wang wrote: >> On 2020/7/16 下午12:13, Zhu, Lingshan wrote: >>> On 7/16/2020 12:02 PM, Jason Wang wrote: >>>> On 2020/7/16 上午11:59, Zhu, Lingshan wrote: >>>>> On 7/16/2020 10:59 AM, Jason Wang wrote: >>>>>> On 2020/7/16 上午9:39, Zhu, Lingshan wrote: >>>>>>> On 7/15/2020 9:43 PM, Jason Wang wrote: >>>>>>>> On 2020/7/12 下午10:52, Zhu Lingshan wrote: >>>>>>>>> Hi All, >>>>>>>>> >>>>>>>>> This series intends to implement IRQ offloading for >>>>>>>>> vhost_vdpa. >>>>>>>>> >>>>>>>>> By the feat of irq forwarding facilities like posted >>>>>>>>> interrupt on X86, irq bypass can  help deliver >>>>>>>>> interrupts to vCPU directly. >>>>>>>>> >>>>>>>>> vDPA devices have dedicated hardware backends like VFIO >>>>>>>>> pass-throughed devices. So it would be possible to setup >>>>>>>>> irq offloading(irq bypass) for vDPA devices and gain >>>>>>>>> performance improvements. >>>>>>>>> >>>>>>>>> In my testing, with this feature, we can save 0.1ms >>>>>>>>> in a ping between two VFs on average. >>>>>>>> Hi Lingshan: >>>>>>>> >>>>>>>> During the virtio-networking meeting, Michael spots >>>>>>>> two possible issues: >>>>>>>> >>>>>>>> 1) do we need an new uAPI to stop the irq offloading? >>>>>>>> 2) can interrupt lost during the eventfd ctx? >>>>>>>> >>>>>>>> For 1) I think we probably not, we can allocate an >>>>>>>> independent eventfd which does not map to MSIX. So >>>>>>>> the consumer can't match the producer and we >>>>>>>> fallback to eventfd based irq. >>>>>>> Hi Jason, >>>>>>> >>>>>>> I wonder why we need to stop irq offloading, but if we >>>>>>> need to do so, maybe a new uAPI would be more intuitive >>>>>>> to me, >>>>>>> but why and who(user? qemu?) shall initialize this >>>>>>> process, based on what kinda of basis to make the >>>>>>> decision? >>>>>> The reason is we may want to fallback to software datapath >>>>>> for some reason (e.g software assisted live migration). In >>>>>> this case we need intercept device write to used ring so we >>>>>> can not offloading virtqueue interrupt in this case. >>>>> so add a VHOST_VDPA_STOP_IRQ_OFFLOADING? Then do we need a >>>>> VHOST_VDPA_START_IRQ_OFFLOADING, then let userspace fully >>>>> control this? Or any better approaches? >>>> Probably not, it's as simple as allocating another eventfd (but not >>>> irqfd), and pass it to vhost-vdpa. Then the offloading is disabled >>>> since it doesn't have a consumer. >>> OK, sounds like QEMU work, no need to take care in this series, right? >> That's my understanding. >> >> Thanks > Let's confirm a switch happens atomically so each interrupt > is sent either to eventfd to guest directly though. I think it's safe since: 1) we don't alloc/free interrupt during the eventfd change 2) The irte is modified automatically through cmpxchg_double() in modify_irte(), so the interrupt is either remapping to eventfd or pi descriptor Thanks > From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH 0/7] *** IRQ offloading for vDPA *** Date: Thu, 16 Jul 2020 16:06:23 +0800 Message-ID: <918ef7c7-852e-6c0a-ed0d-fac3fa6752e4@redhat.com> References: <1594565524-3394-1-git-send-email-lingshan.zhu@intel.com> <70244d80-08a4-da91-3226-7bfd2019467e@redhat.com> <97032c51-3265-c94a-9ce1-f42fcc6d3075@intel.com> <77318609-85ef-f169-2a1e-500473976d84@redhat.com> <29ab6da8-ed8e-6b91-d658-f3d240543b29@intel.com> <1e91d9dd-d787-beff-2c14-9c76ffc3b285@redhat.com> <67c4c41d-9e95-2270-4acb-6f04668c34fa@redhat.com> <20200716021435-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20200716021435-mutt-send-email-mst@kernel.org> Content-Language: en-US Sender: kvm-owner@vger.kernel.org To: "Michael S. Tsirkin" Cc: "Zhu, Lingshan" , alex williamson , pbonzini@redhat.com, sean.j.christopherson@intel.com, wanpengli@tencent.com, "virtualization@lists.linux-foundation.org" , "netdev@vger.kernel.org" , "kvm@vger.kernel.org" , dan daly List-Id: virtualization@lists.linuxfoundation.org On 2020/7/16 下午2:15, Michael S. Tsirkin wrote: > On Thu, Jul 16, 2020 at 12:20:09PM +0800, Jason Wang wrote: >> On 2020/7/16 下午12:13, Zhu, Lingshan wrote: >>> On 7/16/2020 12:02 PM, Jason Wang wrote: >>>> On 2020/7/16 上午11:59, Zhu, Lingshan wrote: >>>>> On 7/16/2020 10:59 AM, Jason Wang wrote: >>>>>> On 2020/7/16 上午9:39, Zhu, Lingshan wrote: >>>>>>> On 7/15/2020 9:43 PM, Jason Wang wrote: >>>>>>>> On 2020/7/12 下午10:52, Zhu Lingshan wrote: >>>>>>>>> Hi All, >>>>>>>>> >>>>>>>>> This series intends to implement IRQ offloading for >>>>>>>>> vhost_vdpa. >>>>>>>>> >>>>>>>>> By the feat of irq forwarding facilities like posted >>>>>>>>> interrupt on X86, irq bypass can  help deliver >>>>>>>>> interrupts to vCPU directly. >>>>>>>>> >>>>>>>>> vDPA devices have dedicated hardware backends like VFIO >>>>>>>>> pass-throughed devices. So it would be possible to setup >>>>>>>>> irq offloading(irq bypass) for vDPA devices and gain >>>>>>>>> performance improvements. >>>>>>>>> >>>>>>>>> In my testing, with this feature, we can save 0.1ms >>>>>>>>> in a ping between two VFs on average. >>>>>>>> Hi Lingshan: >>>>>>>> >>>>>>>> During the virtio-networking meeting, Michael spots >>>>>>>> two possible issues: >>>>>>>> >>>>>>>> 1) do we need an new uAPI to stop the irq offloading? >>>>>>>> 2) can interrupt lost during the eventfd ctx? >>>>>>>> >>>>>>>> For 1) I think we probably not, we can allocate an >>>>>>>> independent eventfd which does not map to MSIX. So >>>>>>>> the consumer can't match the producer and we >>>>>>>> fallback to eventfd based irq. >>>>>>> Hi Jason, >>>>>>> >>>>>>> I wonder why we need to stop irq offloading, but if we >>>>>>> need to do so, maybe a new uAPI would be more intuitive >>>>>>> to me, >>>>>>> but why and who(user? qemu?) shall initialize this >>>>>>> process, based on what kinda of basis to make the >>>>>>> decision? >>>>>> The reason is we may want to fallback to software datapath >>>>>> for some reason (e.g software assisted live migration). In >>>>>> this case we need intercept device write to used ring so we >>>>>> can not offloading virtqueue interrupt in this case. >>>>> so add a VHOST_VDPA_STOP_IRQ_OFFLOADING? Then do we need a >>>>> VHOST_VDPA_START_IRQ_OFFLOADING, then let userspace fully >>>>> control this? Or any better approaches? >>>> Probably not, it's as simple as allocating another eventfd (but not >>>> irqfd), and pass it to vhost-vdpa. Then the offloading is disabled >>>> since it doesn't have a consumer. >>> OK, sounds like QEMU work, no need to take care in this series, right? >> That's my understanding. >> >> Thanks > Let's confirm a switch happens atomically so each interrupt > is sent either to eventfd to guest directly though. I think it's safe since: 1) we don't alloc/free interrupt during the eventfd change 2) The irte is modified automatically through cmpxchg_double() in modify_irte(), so the interrupt is either remapping to eventfd or pi descriptor Thanks >