From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:50656) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UO8Bu-0000IF-CC for qemu-devel@nongnu.org; Fri, 05 Apr 2013 11:04:36 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UO8Bs-0006O8-7s for qemu-devel@nongnu.org; Fri, 05 Apr 2013 11:04:34 -0400 Received: from mx1.redhat.com ([209.132.183.28]:18540) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UO8Br-0006Ny-Vy for qemu-devel@nongnu.org; Fri, 05 Apr 2013 11:04:32 -0400 Message-ID: <515EE7FE.9090202@redhat.com> Date: Fri, 05 Apr 2013 09:04:30 -0600 From: Eric Blake MIME-Version: 1.0 References: <1365169560-11012-1-git-send-email-aliguori@us.ibm.com> In-Reply-To: <1365169560-11012-1-git-send-email-aliguori@us.ibm.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="----enig2KVTDQTIUCTSILCOSMSCB" Subject: Re: [Qemu-devel] [PATCH] main-loop: drop the BQL if the I/O appears to be spinning List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: Paolo Bonzini , qemu-devel@nongnu.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) ------enig2KVTDQTIUCTSILCOSMSCB Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 04/05/2013 07:46 AM, Anthony Liguori wrote: > The char-flow refactoring introduced a busy-wait that depended on > an action from the VCPU thread. However, the VCPU thread could > never take that action because the busy-wait starved the VCPU thread > of the BQL because it never dropped the mutex while running select. >=20 > Paolo doesn't want to drop this optimization for fear that we will > stop detecting these busy waits. I'm afraid to keep this optimization > even with the busy-wait fixed because I think a similar problem can > occur just with heavy I/O thread load manifesting itself as VCPU pauses= =2E >=20 > As a compromise, introduce an artificial timeout after a thousand > iterations but print a rate limited warning when this happens. This > let's us still detect when this condition occurs without it being > a fatal error. >=20 > + * print a message to the screen. If we run into this condition, = create > + * an fake timeout in order to give the VCPU threads a chance to r= un. s/an fake/a fake/ --=20 Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org ------enig2KVTDQTIUCTSILCOSMSCB Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.13 (GNU/Linux) Comment: Public key at http://people.redhat.com/eblake/eblake.gpg Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBCAAGBQJRXuf+AAoJEKeha0olJ0Nq6zcIAIULSim0rgvN7LfgRMVsNvnh jqQYKfPEIwO0lYmNL6VxC1Tr8lz9pOQlY1Bg4a+9nHfDUYyXgGfK0LDLyIjBraVh PiVcs9M7zJzJ5ZYHmieZ+EhaH7tNB0iXtGBnuWUGYLhhnMhG7qq0m3pgLxqvjv1A 3PccgMG+QPH8TRzq3AjL0VwGLOfDjMpL5VpF/XsXDFno5O9vyVoUx3lDZsdquHg2 H1rsJ/kjTWIn/FbDcp1ypcfR/r+NrvA6sP/P26/VoHnvXk+MDvydKiFcRYxeNkiK /WWzg5NCkcP3HMiMGom7s0r0FcL8MgJuQirkGW2h6sZkpbg71LCCNwDvJHuDZl8= =cKwJ -----END PGP SIGNATURE----- ------enig2KVTDQTIUCTSILCOSMSCB--