From mboxrd@z Thu Jan 1 00:00:00 1970 From: Siwei Liu Subject: Re: Re: [Qemu-devel] [PATCH v3 0/3] Use of unique identifier for pairing virtio and passthrough devices... Date: Tue, 10 Jul 2018 11:56:28 -0700 Message-ID: References: <20180629221907.3662-1-venu.busireddy@oracle.com> <20180702161404.GA2339@rkaganb.sw.ru> <449f1449-ddf6-cd95-976c-14d04d8d503a@oracle.com> <20180703095825.GC30904@rkaganb.sw.ru> <20180709130035.GA6271@rkaganb.sw.ru> <9136094e-a510-4201-7c71-d1c49226fa5f@oracle.com> <20180710045614-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Cc: si-wei liu , Roman Kagan , Venu Busireddy , Marcel Apfelbaum , virtio-dev@lists.oasis-open.org, qemu-devel@nongnu.org, "Samudrala, Sridhar" , Alexander Duyck , Netdev To: "Michael S. Tsirkin" Return-path: Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: In-Reply-To: <20180710045614-mutt-send-email-mst@kernel.org> List-Id: netdev.vger.kernel.org On Mon, Jul 9, 2018 at 6:58 PM, Michael S. Tsirkin wrote: > On Mon, Jul 09, 2018 at 06:11:53PM -0700, si-wei liu wrote: >> What do we buy >> for using a random address during initial discovery and requiring VF to >> complete the handshake? > > I don't see advantages to using a random address that is then > changed either: changing a MAC causes network downtime for most users. > Definitely. I see Linux host stack fundamentally different with Windows, it's non-sense to duplicate what Hyper-V is doing especially if there's no extra benefit. >> Less network downtime during datapath switching? >> Sorry but that's not a key factor at all for our main goal - live migration. > > Isn't avoiding downtime what makes the migration "live"? > If you don't care about it at all just remove the device > and migrate without all these tricks. Apparently this downtime is not avoidable even if guest initiates the switch-over when it is done on Linux host stack. Unless the NIC supports adding duplicate MAC filters with one has higher priority than the other when both are present. I feel there's very little or perhaps zero improvement for the downtime if moving to a guest-initiated datapath switching model. However, since this downtime is intermittent and generally unnoticeable with a few packet drops, network should be resilient in recovering from the drops. My point is that unless we can move to a datapath switching model with zero downtime theoretically, this kind of minor optimization offers very little help in general. Regards, -Siwei > > > -- > MST > > --------------------------------------------------------------------- > To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org > For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org > From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:36039) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fcxoN-0004cL-Gs for qemu-devel@nongnu.org; Tue, 10 Jul 2018 14:56:32 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fcxoM-0004to-Mm for qemu-devel@nongnu.org; Tue, 10 Jul 2018 14:56:31 -0400 Received: from mail-io0-x241.google.com ([2607:f8b0:4001:c06::241]:36340) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1fcxoM-0004te-Gz for qemu-devel@nongnu.org; Tue, 10 Jul 2018 14:56:30 -0400 Received: by mail-io0-x241.google.com with SMTP id k3-v6so21351856iog.3 for ; Tue, 10 Jul 2018 11:56:30 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20180710045614-mutt-send-email-mst@kernel.org> References: <20180629221907.3662-1-venu.busireddy@oracle.com> <20180702161404.GA2339@rkaganb.sw.ru> <449f1449-ddf6-cd95-976c-14d04d8d503a@oracle.com> <20180703095825.GC30904@rkaganb.sw.ru> <20180709130035.GA6271@rkaganb.sw.ru> <9136094e-a510-4201-7c71-d1c49226fa5f@oracle.com> <20180710045614-mutt-send-email-mst@kernel.org> From: Siwei Liu Date: Tue, 10 Jul 2018 11:56:28 -0700 Message-ID: Content-Type: text/plain; charset="UTF-8" Subject: Re: [Qemu-devel] [virtio-dev] Re: [PATCH v3 0/3] Use of unique identifier for pairing virtio and passthrough devices... List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: si-wei liu , Roman Kagan , Venu Busireddy , Marcel Apfelbaum , virtio-dev@lists.oasis-open.org, qemu-devel@nongnu.org, "Samudrala, Sridhar" , Alexander Duyck , Netdev On Mon, Jul 9, 2018 at 6:58 PM, Michael S. Tsirkin wrote: > On Mon, Jul 09, 2018 at 06:11:53PM -0700, si-wei liu wrote: >> What do we buy >> for using a random address during initial discovery and requiring VF to >> complete the handshake? > > I don't see advantages to using a random address that is then > changed either: changing a MAC causes network downtime for most users. > Definitely. I see Linux host stack fundamentally different with Windows, it's non-sense to duplicate what Hyper-V is doing especially if there's no extra benefit. >> Less network downtime during datapath switching? >> Sorry but that's not a key factor at all for our main goal - live migration. > > Isn't avoiding downtime what makes the migration "live"? > If you don't care about it at all just remove the device > and migrate without all these tricks. Apparently this downtime is not avoidable even if guest initiates the switch-over when it is done on Linux host stack. Unless the NIC supports adding duplicate MAC filters with one has higher priority than the other when both are present. I feel there's very little or perhaps zero improvement for the downtime if moving to a guest-initiated datapath switching model. However, since this downtime is intermittent and generally unnoticeable with a few packet drops, network should be resilient in recovering from the drops. My point is that unless we can move to a datapath switching model with zero downtime theoretically, this kind of minor optimization offers very little help in general. Regards, -Siwei > > > -- > MST > > --------------------------------------------------------------------- > To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org > For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-dev-return-4671-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 69FC4985BF3 for ; Tue, 10 Jul 2018 18:56:30 +0000 (UTC) MIME-Version: 1.0 In-Reply-To: <20180710045614-mutt-send-email-mst@kernel.org> References: <20180629221907.3662-1-venu.busireddy@oracle.com> <20180702161404.GA2339@rkaganb.sw.ru> <449f1449-ddf6-cd95-976c-14d04d8d503a@oracle.com> <20180703095825.GC30904@rkaganb.sw.ru> <20180709130035.GA6271@rkaganb.sw.ru> <9136094e-a510-4201-7c71-d1c49226fa5f@oracle.com> <20180710045614-mutt-send-email-mst@kernel.org> From: Siwei Liu Date: Tue, 10 Jul 2018 11:56:28 -0700 Message-ID: Content-Type: text/plain; charset="UTF-8" Subject: Re: [virtio-dev] Re: [Qemu-devel] [PATCH v3 0/3] Use of unique identifier for pairing virtio and passthrough devices... To: "Michael S. Tsirkin" Cc: si-wei liu , Roman Kagan , Venu Busireddy , Marcel Apfelbaum , virtio-dev@lists.oasis-open.org, qemu-devel@nongnu.org, "Samudrala, Sridhar" , Alexander Duyck , Netdev List-ID: On Mon, Jul 9, 2018 at 6:58 PM, Michael S. Tsirkin wrote: > On Mon, Jul 09, 2018 at 06:11:53PM -0700, si-wei liu wrote: >> What do we buy >> for using a random address during initial discovery and requiring VF to >> complete the handshake? > > I don't see advantages to using a random address that is then > changed either: changing a MAC causes network downtime for most users. > Definitely. I see Linux host stack fundamentally different with Windows, it's non-sense to duplicate what Hyper-V is doing especially if there's no extra benefit. >> Less network downtime during datapath switching? >> Sorry but that's not a key factor at all for our main goal - live migration. > > Isn't avoiding downtime what makes the migration "live"? > If you don't care about it at all just remove the device > and migrate without all these tricks. Apparently this downtime is not avoidable even if guest initiates the switch-over when it is done on Linux host stack. Unless the NIC supports adding duplicate MAC filters with one has higher priority than the other when both are present. I feel there's very little or perhaps zero improvement for the downtime if moving to a guest-initiated datapath switching model. However, since this downtime is intermittent and generally unnoticeable with a few packet drops, network should be resilient in recovering from the drops. My point is that unless we can move to a datapath switching model with zero downtime theoretically, this kind of minor optimization offers very little help in general. Regards, -Siwei > > > -- > MST > > --------------------------------------------------------------------- > To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org > For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org > --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org