From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:43101) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SCFmo-0001sH-5k for qemu-devel@nongnu.org; Mon, 26 Mar 2012 15:41:06 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SCFmj-000441-7F for qemu-devel@nongnu.org; Mon, 26 Mar 2012 15:41:01 -0400 Received: from spam1.wiktel.com ([69.89.207.151]:41407) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SCFmj-000439-2A for qemu-devel@nongnu.org; Mon, 26 Mar 2012 15:40:57 -0400 From: Richard Laager In-Reply-To: <20120324153040.GC13014@lst.de> References: <1331226917-6658-1-git-send-email-pbonzini@redhat.com> <1331226917-6658-7-git-send-email-pbonzini@redhat.com> <4F5A31B2.3050701@redhat.com> <4F5A46A1.4000508@redhat.com> <1331402560.8577.46.camel@watermelon.coderich.net> <4F5DEBCE.3040409@redhat.com> <1331665990.24052.42.camel@watermelon.coderich.net> <4F604B98.9090606@redhat.com> <4F60889F.6030401@redhat.com> <4F608B9A.8040406@redhat.com> <20120324153040.GC13014@lst.de> Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-n73LHf1J2eapcoA9/jxv" Date: Mon, 26 Mar 2012 14:40:48 -0500 Message-ID: <1332790848.3486.27.camel@watermelon.coderich.net> Mime-Version: 1.0 Subject: Re: [Qemu-devel] [RFC PATCH 06/17] block: use bdrv_{co, aio}_discard for write_zeroes operations List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Christoph Hellwig Cc: qemu-devel@nongnu.org --=-n73LHf1J2eapcoA9/jxv Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sat, 2012-03-24 at 16:30 +0100, Christoph Hellwig wrote: > On Wed, Mar 14, 2012 at 01:14:18PM +0100, Paolo Bonzini wrote: > >=20 > > Note that the discard granularity is only a hint, so it's really more a > > maximum suggested value than a granularity. Outside of a cluster > > boundary the format would still have to write zeros manually. > >=20 > > Also, Linux for example will only round the number of sectors down to > > the granularity, not the start sector. >=20 > Which really is more of a bug than a feature. The current discard > implementation in Linux is still very poor. The disk protocols do not require the granularity to be respected. It is *only a hint*. Therefore, QEMU has to handle non-aligned discards. It doesn't really matter what we wish was the case; this is the reality. --=20 Richard --=-n73LHf1J2eapcoA9/jxv Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iEYEABECAAYFAk9wxkAACgkQbfU6uV4fG879cgCdHc+iCOsn3SKwME0QK7aSvJz7 iasAnRUlt/8rhl+Q5lqm69bjul3fncxb =3Bg/ -----END PGP SIGNATURE----- --=-n73LHf1J2eapcoA9/jxv--