From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1ME6ra-0000qx-Kx for qemu-devel@nongnu.org; Tue, 09 Jun 2009 15:20:02 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1ME6rU-0000qO-Nr for qemu-devel@nongnu.org; Tue, 09 Jun 2009 15:20:01 -0400 Received: from [199.232.76.173] (port=55285 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1ME6rU-0000qK-LD for qemu-devel@nongnu.org; Tue, 09 Jun 2009 15:19:56 -0400 Received: from fmmailgate02.web.de ([217.72.192.227]:38611) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1ME6rU-000852-3C for qemu-devel@nongnu.org; Tue, 09 Jun 2009 15:19:56 -0400 Message-ID: <4A2EB5D2.8030107@web.de> Date: Tue, 09 Jun 2009 21:19:46 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <1244565768-9103-1-git-send-email-amit.shah@redhat.com> <1244565768-9103-2-git-send-email-amit.shah@redhat.com> <1244565768-9103-3-git-send-email-amit.shah@redhat.com> <1244565768-9103-4-git-send-email-amit.shah@redhat.com> <4A2E98AD.2090904@siemens.com> <20090609181522.GA11485@amd.home.annexia.org> In-Reply-To: <20090609181522.GA11485@amd.home.annexia.org> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig59B0111FA0D09B42325C0E9F" Sender: jan.kiszka@web.de Subject: [Qemu-devel] Re: [PATCH] virtio-serial: PCI device for simple host <-> guest communication List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Richard W.M. Jones" Cc: Amit Shah , qemu-devel@nongnu.org This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig59B0111FA0D09B42325C0E9F Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Richard W.M. Jones wrote: > On Tue, Jun 09, 2009 at 07:15:25PM +0200, Jan Kiszka wrote: >> Amit Shah wrote: >>> This interface presents a char device from which bits can be >>> sent and read. >>> >>> Sample uses for such a device can be obtaining info from the >>> guest like the file systems used, apps installed, etc. for >>> offline usage and logged-in users, clipboard copy-paste, etc. >>> for online usage. >> Out of curiosity: What is the advantage over instantiating a multiport= >> 16550A PCI card? Will those channels be so performance critical? >=20 > 16550A has a couple of problems: The fixed sized FIFO (16 bytes) can > cause problems if you send data too quickly. (I've seen this problem > when sending too much data from host to the guest, but I can't find > the bug report right now ...). If you buy a real 16550A card with high-speed support (eg. 1 MBit/s), you get larger FIFOs (eg. 256 byte). Thresholds are scaled correspondingly by such cards. So there would be no problem in extending this in QEMU as well, ie. making it a parameter to the init function. > Secondly UARTs are complicated to > emulate compared to a clean virtio device. Would we be happy with the > address space taken up and amount of emulation going on once we had, > say, 16 emulated ports? Memory-mapped 16550As do not suffer from such a limitation. >=20 > On the other hand, multiport cards don't require special drivers in > the guest ... That's what raised my interest: What benefit of a virtio-serial can over-compensate this advantage of standard hardware? Jan --------------enig59B0111FA0D09B42325C0E9F Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org iEYEARECAAYFAkoutdYACgkQniDOoMHTA+myMgCeMUphVQAH4zWSK5jiIZVZE5mX +ogAn2NOoCGYFRdPC7zFjDIq39z46Tbn =KZ2O -----END PGP SIGNATURE----- --------------enig59B0111FA0D09B42325C0E9F--