From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:45569) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gtgAk-0005bb-8l for qemu-devel@nongnu.org; Tue, 12 Feb 2019 17:05:01 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gtgAj-0001pb-0R for qemu-devel@nongnu.org; Tue, 12 Feb 2019 17:04:58 -0500 References: <20190212200750.27521-1-jsnow@redhat.com> <44d4452d-8b94-205a-dc28-c617be80c29c@redhat.com> <87241634-5a14-f943-8446-07bd34f12aff@redhat.com> From: Eric Blake Message-ID: <445f2f21-d769-14f5-2259-80b3ea6e9988@redhat.com> Date: Tue, 12 Feb 2019 16:04:31 -0600 MIME-Version: 1.0 In-Reply-To: <87241634-5a14-f943-8446-07bd34f12aff@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="b33FJip739WpUWkNsbwQjuxGLndZV9qgU" Subject: Re: [Qemu-devel] [PATCH v2] blockdev: acquire aio_context for bitmap add/remove List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: John Snow , qemu-block@nongnu.org, qemu-devel@nongnu.org Cc: Kevin Wolf , pbonzini@redhat.com, vsementsov@virtuozzo.com, Markus Armbruster , Max Reitz This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --b33FJip739WpUWkNsbwQjuxGLndZV9qgU From: Eric Blake To: John Snow , qemu-block@nongnu.org, qemu-devel@nongnu.org Cc: Kevin Wolf , pbonzini@redhat.com, vsementsov@virtuozzo.com, Markus Armbruster , Max Reitz Message-ID: <445f2f21-d769-14f5-2259-80b3ea6e9988@redhat.com> Subject: Re: [PATCH v2] blockdev: acquire aio_context for bitmap add/remove References: <20190212200750.27521-1-jsnow@redhat.com> <44d4452d-8b94-205a-dc28-c617be80c29c@redhat.com> <87241634-5a14-f943-8446-07bd34f12aff@redhat.com> In-Reply-To: <87241634-5a14-f943-8446-07bd34f12aff@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 2/12/19 3:37 PM, John Snow wrote: >=20 >=20 > On 2/12/19 3:16 PM, Eric Blake wrote: >> On 2/12/19 2:07 PM, John Snow wrote: >>> When bitmaps are persistent, they may incur a disk read or write when= bitmaps >>> are added or removed. For configurations like virtio-dataplane, faili= ng to >>> acquire this lock will abort QEMU when disk IO occurs. >>> >>> We used to acquire aio_context as part of the bitmap lookup, so re-in= troduce >>> the lock for just the cases that have an IO penalty. >> >> It would be nice to call out which commit id dropped the aio_context >> acquisition during bitmap lookup (making it easier to analyze how long= >> this has broken, and which downstream builds need the backport. >> >=20 > OK, I will amend this. >=20 > Looks like: >=20 > commit 2119882c7eb7e2c612b24fc0c8d86f5887d6f1c3 > Author: Paolo Bonzini > Date: Mon Jun 5 14:39:03 2017 +0200 >=20 > since 2.10. Hmm. block-dirty-bitmap-add's "persistent":true parameter was also added in 2.10 in commit fd5ae4cc. In fact, 2119882c was made at a time when there were not persistent bitmaps; so I guess that this means we have always been broken since fd5ae4cc. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org --b33FJip739WpUWkNsbwQjuxGLndZV9qgU Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEccLMIrHEYCkn0vOqp6FrSiUnQ2oFAlxjQu8ACgkQp6FrSiUn Q2o6SAf/eqTwF5W/m0rscZXHMLl9Si+CTvdFIsu8+fe8CHWJyhvnVVmziI1lhFVc 1RapKkZkP/tPOBMHwOagZgL99wIZpqQhLt6d2tUmpniwrFYo64i96LmbbeHJjR5a oTmweFb1HpBrfWM8gGV+6NXnDUCZJVbWPkfOnzi0e65wip9p5ZosG+AJ4bxmiEzG rgxNXJDBzUdJhlbgOXqkHBJe3Jw7Fab7TNJB9/bcLvIFWTRRg7xdFIFhhLLyNYeW XZ+vam8pC+ILvJudqYrVfvvS4FpTxP+ffURCpx+PvJtt7P6VSNShVkutNK5ap6NC Dfull1G3gWOIWMBqlD4HYGwLGVSK+Q== =dIDc -----END PGP SIGNATURE----- --b33FJip739WpUWkNsbwQjuxGLndZV9qgU--