From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58123) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ebaV2-0000nx-Dt for qemu-devel@nongnu.org; Tue, 16 Jan 2018 18:18:38 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ebaV1-0004x4-8t for qemu-devel@nongnu.org; Tue, 16 Jan 2018 18:18:36 -0500 References: <8525e16caa2fecac537aa62a449ea8626f5c7e36.1513342045.git.berto@igalia.com> From: Eric Blake Message-ID: <6f573609-a04e-b3c5-6359-b6e08b138549@redhat.com> Date: Tue, 16 Jan 2018 17:18:25 -0600 MIME-Version: 1.0 In-Reply-To: <8525e16caa2fecac537aa62a449ea8626f5c7e36.1513342045.git.berto@igalia.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="cCGzdW02xEfIvdUgk3kvLxIAIWdN8Xfrv" Subject: Re: [Qemu-devel] [PATCH v2 31/32] qcow2: Allow configuring the L2 slice size List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alberto Garcia , qemu-devel@nongnu.org Cc: Kevin Wolf , "Denis V . Lunev" , qemu-block@nongnu.org, Max Reitz This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --cCGzdW02xEfIvdUgk3kvLxIAIWdN8Xfrv From: Eric Blake To: Alberto Garcia , qemu-devel@nongnu.org Cc: Kevin Wolf , "Denis V . Lunev" , qemu-block@nongnu.org, Max Reitz Message-ID: <6f573609-a04e-b3c5-6359-b6e08b138549@redhat.com> Subject: Re: [Qemu-devel] [PATCH v2 31/32] qcow2: Allow configuring the L2 slice size References: <8525e16caa2fecac537aa62a449ea8626f5c7e36.1513342045.git.berto@igalia.com> In-Reply-To: <8525e16caa2fecac537aa62a449ea8626f5c7e36.1513342045.git.berto@igalia.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 12/15/2017 06:53 AM, Alberto Garcia wrote: > Now that the code is ready to handle L2 slices we can finally add an > option to allow configuring their size. >=20 > An L2 slice is the portion of an L2 table that is read by the qcow2 > cache. Until now the cache was always reading full L2 tables, and > since the L2 table size is equal to the cluster size this was not very > efficient with large clusters. Here's a more detailed explanation of > why it makes sense to have smaller cache entries in order to load L2 > data: >=20 > https://lists.gnu.org/archive/html/qemu-block/2017-09/msg00635.html >=20 > This patch introduces a new command-line option to the qcow2 driver > named l2-cache-entry-size (cf. l2-cache-size). The cache entry size > has the same restrictions as the cluster size: it must be a power of > two and it has the same range of allowed values, with the additional > requirement that it must not be larger than the cluster size. >=20 > The L2 cache entry size (L2 slice size) remains equal to the cluster > size for now by default, so this feature must be explicitly enabled. > Although my tests show that 4KB slices consistently improve > performance and give the best results, let's wait and make more tests > with different cluster sizes before deciding on an optimal default. >=20 > Signed-off-by: Alberto Garcia > --- > block/qcow2-cache.c | 10 ++++++++-- > block/qcow2.c | 33 +++++++++++++++++++++++++++------ > block/qcow2.h | 4 +++- > 3 files changed, 38 insertions(+), 9 deletions(-) Is there a QMP counterpart to the command-line option? I suspect Kevin's work on making a QMP command for image creation will also be impacted. I haven't reviewed the patch closely, yet. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org --cCGzdW02xEfIvdUgk3kvLxIAIWdN8Xfrv Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEzBAEBCAAdFiEEccLMIrHEYCkn0vOqp6FrSiUnQ2oFAlpeiEEACgkQp6FrSiUn Q2qFOAf8Do5WCqrgtRgLoIXRjeZ8TE9jm/c+2E7KHcVK2Qr9VVAsIuc4vrS7IyRE YXwZWBAh4BOUTZMT4Nx9YwOTh5GZQ1inQ+cRpn6MOCV3jIehta79HzNBjUGsDu/h eW7Nwkbkrw+efJ8dTiZPCHNXEeN8jZEkjmY/9/eDhBKLQDa5tAsnhbFx7HjcqNvm yrRbY4u97WRj9/2jH5yYzbxa9frtrQSUnrc7enLpEzIgILcK/NiMHWF3A/D6z2p1 +81QMQ7VsoUEUcB7KESTnnVs3Z3EKaeLtqMQGPxM0RiWfTiSSElURKgURhMkqWDK 2jyn8wTpOQakSnx/D2cmLU5urFXrFw== =hxCc -----END PGP SIGNATURE----- --cCGzdW02xEfIvdUgk3kvLxIAIWdN8Xfrv--