From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:48503) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SiPpu-0007Ny-KU for qemu-devel@nongnu.org; Sat, 23 Jun 2012 08:53:11 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SiPps-0002UC-Qd for qemu-devel@nongnu.org; Sat, 23 Jun 2012 08:53:10 -0400 Received: from mout.web.de ([212.227.17.11]:53309) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SiPps-0002U5-GR for qemu-devel@nongnu.org; Sat, 23 Jun 2012 08:53:08 -0400 Message-ID: <4FE5BC31.8000006@web.de> Date: Sat, 23 Jun 2012 14:53:05 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <4FE58C20.4020803@web.de> <4FE5BA8F.7050405@web.de> In-Reply-To: <4FE5BA8F.7050405@web.de> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigA56AD4173F251CEF84507C97" Subject: Re: [Qemu-devel] MMIO coalescing of the i82378 bridge List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?ISO-8859-1?Q?Andreas_F=E4rber?= Cc: =?ISO-8859-1?Q?Herv=E9_Poussineau?= , qemu-devel This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigA56AD4173F251CEF84507C97 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 2012-06-23 14:46, Andreas F=E4rber wrote: > Hi Jan, >=20 > Am 23.06.2012 11:28, schrieb Jan Kiszka: >> just stumbled over the memory_region_set_coalescing in pci_i82378_init= : >> What ISA devices are affected by this? It looks a bit strange to me as= >> the MMIO requests are apparently mapped on PIO requests, and we don't >> have PIO coalescing on x86. Depending on the target device on PREP, th= is >> may have some unexpected side effects. Or is only framebuffer memory >> addressed this way? >=20 > I only remember touching that line to rebase it onto either Memory API > or QOM. The i82378 is the sole PCI-ISA bridge so all ISA devices will b= e > affected by it, which is pretty much everything except VGA iirc. > The upcoming pc87312(?) Super I/O also would be attached to it, > replacing some of the bogus I/O in the current "prep" machine. >=20 > I'm not familiar with what this option affects. What unexpected side > effects would you expect? :) Simple example: You write to the PIT to start/stop a timer, but this transaction is now delayed until the next coalesced buffer flush. IOW, there surely exit write operations that must not be reordered /wrt to the VCPU execution flow. I would recommend to drop coalescing, even more if its benefit is not clear. Jan --------------enigA56AD4173F251CEF84507C97 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.16 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk/lvDEACgkQitSsb3rl5xT40ACffSDU0GDJhv4QTTu8zFR4/DCR do0AoKoYa/wUOB+YTPvAKlFx1e10RrDW =0Axa -----END PGP SIGNATURE----- --------------enigA56AD4173F251CEF84507C97--