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[54.240.197.238]) by smtp.gmail.com with ESMTPSA id s4sm2429352edw.19.2020.04.06.00.50.22 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 06 Apr 2020 00:50:22 -0700 (PDT) From: Paul Durrant X-Google-Original-From: "Paul Durrant" To: "'Dongli Zhang'" , "'Andrew Cooper'" , "'Anastassios Nanos'" , References: In-Reply-To: Subject: RE: Live migration and PV device handling Date: Mon, 6 Apr 2020 08:50:21 +0100 Message-ID: <001301d60be8$06afa1a0$140ee4e0$@xen.org> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Mailer: Microsoft Outlook 16.0 Content-Language: en-gb Thread-Index: AQJ9hFEeoa99jEIZ37IjX6uiVjJ3WQHz1sx0AqxQcWKm98VpMA== X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Reply-To: paul@xen.org Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" > -----Original Message----- > From: Xen-devel On Behalf Of = Dongli Zhang > Sent: 03 April 2020 23:33 > To: Andrew Cooper ; Anastassios Nanos = ; xen- > devel@lists.xen.org > Subject: Re: Live migration and PV device handling >=20 > Hi Andrew, >=20 > On 4/3/20 5:42 AM, Andrew Cooper wrote: > > On 03/04/2020 13:32, Anastassios Nanos wrote: > >> Hi all, > >> > >> I am trying to understand how live-migration happens in xen. I am > >> looking in the HVM guest case and I have dug into the relevant = parts > >> of the toolstack and the hypervisor regarding memory, vCPU context > >> etc. > >> > >> In particular, I am interested in how PV device migration happens. = I > >> assume that the guest is not aware of any suspend/resume operations > >> being done > > > > Sadly, this assumption is not correct. HVM guests with PV drivers > > currently have to be aware in exactly the same way as PV guests. > > > > Work is in progress to try and address this. See > > = https://xenbits.xen.org/gitweb/?p=3Dxen.git;a=3Dcommitdiff;h=3D775a02452d= df3a6889690de90b1a94eb29c3c732 > > (sorry - for some reason that doc isn't being rendered properly in > > https://xenbits.xen.org/docs/ ) > > >=20 > I read below from the commit: >=20 > +* The toolstack choose a randomized domid for initial creation or = default > +migration, but preserve the source domid non-cooperative migration. > +Non-Cooperative migration will have to be denied if the domid is > +unavailable on the target host, but randomization of domid on = creation > +should hopefully minimize the likelihood of this. Non-Cooperative = migration > +to localhost will clearly not be possible. >=20 > Does that indicate while scope of domid_t is shared by a single server = in old > design, the scope of domid_t is shared by a cluster of server in new = design? >=20 > That is, the domid should be unique in the cluster of all servers if = we expect > non-cooperative migration always succeed? >=20 That would be necessary to guarantee success (or rather guarantee no = failure due to domid clash) but the scope of xl/libxl is single serve, = hence randomization is the best we have to reduce clashes to a minimum. Paul