From mboxrd@z Thu Jan 1 00:00:00 1970 From: Laurent Vivier Subject: Re: [PATCH] qemu: use statically allocate 512 byte buffer in the stack for sector in bdrv_commit Date: Mon, 07 Jan 2008 18:05:52 +0100 Message-ID: <1199725552.23380.52.camel@frecb07144> References: <20080104071138.GB9285@tapir> <4781F08E.8060407@qumranet.com> <1199701358.19008.1.camel@frecb07144> <4782034C.4000805@qumranet.com> <1199719004.23380.22.camel@frecb07144> <90eb1dc70801070734l2062cac6r7a7bed1d6d3d2c0c@mail.gmail.com> <1199720749.23380.29.camel@frecb07144> <90eb1dc70801070803w1a863acs75677e707446f79a@mail.gmail.com> <1199723417.23380.43.camel@frecb07144> <90eb1dc70801070842g585cd92dr8a8a383e2f3274df@mail.gmail.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============1870637919==" Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: Javier Guerra Return-path: In-Reply-To: <90eb1dc70801070842g585cd92dr8a8a383e2f3274df-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org --===============1870637919== Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=-BqMsOU6HAFbrjYmXCJ+d" --=-BqMsOU6HAFbrjYmXCJ+d Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Well, in fact, I think you can't use snapshot with cluster filesystem: as each qemu instance will write in its own snapshot and will not see modifications made by other, and I don't think there is currently a way to share snapshot between qemu instances. Laurent Le lundi 07 janvier 2008 =C3=A0 11:42 -0500, Javier Guerra a =C3=A9crit : > On 1/7/08, Laurent Vivier wrote: > > Le lundi 07 janvier 2008 =C3=A0 11:03 -0500, Javier Guerra a =C3=A9crit= : > > > hopefully, it would now work with "-cache=3Doff", don't you think? > > > > Well, I don't think the problem is at the host level but at the guest > > level, because both instances of qemu share the host cache and thus > > first instance should see changes made by the second instance (and > > vice-versa). >=20 > that's what a cluster filesystem is designed to cope with (and in fact ex= pects) >=20 > > There are also some caches at qemu level to emulate DMA, for instance i= n > > hw/ide.c it is MAX_MULT_SECTORS (16) which is 8 kB buffer, perhaps your > > problem is here but "cache=3Doff" doesn't remove this. > > Did you try to change MAX_MULT_SECTORS to 1 ? >=20 > nope, don't know enough of qemu internals... >=20 > but if those caches can be flushed from the guest, the filesystem > should do that when writing its metadata >=20 > > What do you call a "cluster filesystem" ? >=20 > GFS, OCFS2, etc. that is, filesystems that are designed to run on > more than one host with shared block storage. usually that means > FibreChannel or iSCSI, but on VMs, a common backing could work too (at > least in theory). >=20 > Xen manages it, at least on paravirtualized guests; hadn't tried on > HVM guests. maybe the IDE-like emulation is too poor an interface to > handle it. >=20 --=20 ----------------- Laurent.Vivier-6ktuUTfB/bM@public.gmane.org ------------------ "La perfection est atteinte non quand il ne reste rien =C3=A0 ajouter mais quand il ne reste rien =C3=A0 enlever." Saint Exup=C3=A9ry --=-BqMsOU6HAFbrjYmXCJ+d Content-Type: application/pgp-signature; name=signature.asc Content-Description: Ceci est une partie de message =?ISO-8859-1?Q?num=E9riquement?= =?ISO-8859-1?Q?_sign=E9e?= -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iD8DBQBHglvw9Kffa9pFVzwRApLaAKCmCVRy7+EKDQxKQguVHkSRLZAL8gCggB1C 7wOP4Q+PTfahsE8xGCfMejI= =/4qj -----END PGP SIGNATURE----- --=-BqMsOU6HAFbrjYmXCJ+d-- --===============1870637919== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace --===============1870637919== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ kvm-devel mailing list kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org https://lists.sourceforge.net/lists/listinfo/kvm-devel --===============1870637919==--