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Thu, 18 Jun 2020 03:30:47 -0400 X-MC-Unique: m98MpKNJPBCgJEHv93genA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id EEC68DB7C; Thu, 18 Jun 2020 07:30:38 +0000 (UTC) Received: from [10.36.110.7] (unknown [10.36.110.7]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3078A1053B11; Thu, 18 Jun 2020 07:30:35 +0000 (UTC) To: Matan Azrad , "xiaolong.ye@intel.com" , Shahaf Shuler , "amorenoz@redhat.com" , "xiao.w.wang@intel.com" , Slava Ovsiienko , "dev@dpdk.org" Cc: "jasowang@redhat.com" , "lulu@redhat.com" References: <20200514080218.1435344-1-maxime.coquelin@redhat.com> <20200514080218.1435344-10-maxime.coquelin@redhat.com> <0216165f-aedd-06c7-5a90-2cd0d238b143@redhat.com> <97528794-aa14-37da-a5bb-1e1d46e9127a@redhat.com> <64c59e91-79ef-bc55-bc64-1995cfb03c84@redhat.com> <095af180-bb29-e890-5197-8bfbb8ea4c41@redhat.com> <7cdc8505-a667-81a3-b8ed-22dd34b958f7@redhat.com> From: Maxime Coquelin Autocrypt: addr=maxime.coquelin@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Subject: Re: [dpdk-dev] [PATCH 9/9] vhost: only use vDPA config workaround if needed X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On 6/18/20 8:39 AM, Matan Azrad wrote: > HI Maxime > > From: Maxime Coquelin: >> On 6/17/20 1:04 PM, Matan Azrad wrote: >> >>>>> Don’t you think that only enabled queues must be fully initialized >>>>> when >>>> their status is changed from disabled to enabled? >>>>> So, you can assume that disabled queues can stay "not fully initialized"... >>>> >>>> That may work but might not be following the Virtio spec as with 1.0 >>>> we shouldn't process the rings before DRIVER_OK is set (but we cannot >>>> be sure we follow it anyway without SET_STATUS support). >>>> >>>> I propose to cook a patch doing the following: >>>> 1. virtio_is_ready() will only ensure the first queue pair is ready >>>> (i.e. enabled and configured). Meaning that app's new_device callback >>>> and vDPA drivers dev_conf callback will be called with only the first >>>> queue pair configured and enabled. >>>> >>>> 2. Before handling a new vhost-user request, it saves the ready >>>> status for every queue pair. >>>> >>>> 3. Same handling of the requests, except that we won't notify the >>>> vdpa driver and the application of vring state changes in the >>>> VHOST_USER_SET_VRING_ENABLE handler. >>>> >>>> 4. Once the Vhost-user request is handled, it compares the new ready >>>> status foe every queues with the old one and send queue state event >>>> changes accordingly. >>> >>> Looks very nice to me. >> >> Cool! >> >>> More points: >>> By this method some queues may be configured by the set_vring_state >> operation so the next calls are expected to be called for each queue by the >> driver from the set_vring_state callback : >>> 1. rte_vhost_enable_guest_notification >>> This one takes datapath lock so we need to be sure that datapath >> lock is not locked on this queue from the same caller thread (maybe to not >> takes datapath locks when vdpa is configured at all). >> >> Good point, I agree we shouldn't need to use the access lock when vdpa is >> configured. We may want to document that all the control path is assumed to >> be single thread though. >> >> >>> 2. rte_vhost_host_notifier_ctrl >>> This function API is per device and not per queue, maybe we need to >> change this function to be per queue (add new for now and deprecate the >> old one in 20.11). >> >> This one is still experimental, so no issue in reworking the API to make it per >> queue without deprecation notice. >> >>> 3. Need to be sure that if ready queue configuration is changed after >> dev_conf, we should notify it to the driver. (maybe by >> set_vring_state(disabl) and set_vring_state(enable)). >> >> Agree, I'm not sure yet if we should just toggle set_vring_state as you >> proposes, or if we should have a new callback for this. > > Actually, when the queue configuration is changed, there is one moment that configuration is not valid (in the write time). > So maybe it makes sense to toggle. > > But there is one more option: > > It doesn't make sense that after configuration change the QEMU will not send VHOST_USER_SET_VRING_ENABLE massage. Agree. > So maybe we need to call set_vring_state in the next events: > 1. queue becomes ready (enabled and fully configured) - set_vring_state(enable). > 2. queue becomes not ready - set_vring_state(disable). > 3. queue stay ready and VHOST_USER_SET_VRING_ENABLE massage was handled - set_vring_state(enable). > > Then we need to document that every set_vring_state call may point on configuration changes in the queue even if the state was not changed. > > What do you think? I think it is worth a try. Thanks, Maxime