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Fri, 26 Jul 2019 10:50:38 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-116-164.ams2.redhat.com [10.36.116.164]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3248B19D7E; Fri, 26 Jul 2019 10:50:35 +0000 (UTC) To: Kevin Wolf , qemu-block@nongnu.org References: <20190725162704.12622-1-kwolf@redhat.com> <20190725162704.12622-5-kwolf@redhat.com> From: Max Reitz Openpgp: preference=signencrypt Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: <6c00ea43-5b9f-5fb7-3e52-86bcf3933668@redhat.com> Date: Fri, 26 Jul 2019 12:50:34 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.2 MIME-Version: 1.0 In-Reply-To: <20190725162704.12622-5-kwolf@redhat.com> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="MIUOMaStJrWWWO8m9kX8NBy4lzGxV7mKQ" X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Fri, 26 Jul 2019 10:50:38 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH 4/4] block-backend: Queue requests while drained X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: dplotnikov@virtuozzo.com, vsementsov@virtuozzo.com, den@virtuozzo.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --MIUOMaStJrWWWO8m9kX8NBy4lzGxV7mKQ Content-Type: multipart/mixed; boundary="gTLn0QrhM5vCYUwfA1TrrSnBAvpm7K3qL"; protected-headers="v1" From: Max Reitz To: Kevin Wolf , qemu-block@nongnu.org Cc: dplotnikov@virtuozzo.com, vsementsov@virtuozzo.com, den@virtuozzo.com, qemu-devel@nongnu.org Message-ID: <6c00ea43-5b9f-5fb7-3e52-86bcf3933668@redhat.com> Subject: Re: [PATCH 4/4] block-backend: Queue requests while drained References: <20190725162704.12622-1-kwolf@redhat.com> <20190725162704.12622-5-kwolf@redhat.com> In-Reply-To: <20190725162704.12622-5-kwolf@redhat.com> --gTLn0QrhM5vCYUwfA1TrrSnBAvpm7K3qL Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 25.07.19 18:27, Kevin Wolf wrote: > This fixes device like IDE that can still start new requests from I/O *devices > handlers in the CPU thread while the block backend is drained. >=20 > The basic assumption is that in a drain section, no new requests should= > be allowed through a BlockBackend (blk_drained_begin/end don't exist, > we get drain sections only on the node level). However, there are two > special cases where requests should not be queued: >=20 > 1. Block jobs: We already make sure that block jobs are paused in a > drain section, so they won't start new requests. However, if the > drain_begin is called on the job's BlockBackend first, it can happen= > that we deadlock because the job stays busy until it reaches a pause= > point - which it can't if it's requests aren't processed any more. >=20 > The proper solution here would be to make all requests through the > job's filter node instead of using a BlockBackend. For now, just > disabling request queuin on the job BlockBackend is simpler. Yep, seems reasonable. (We=E2=80=99d need a relationship that a BB is owned by some job, and the= n pause the job when the BB is drained, I suppose. But that=E2=80=99s exactly accomplished by not making the job use a BB, but its BdrvChild references instead.) > 2. In test cases where making requests through bdrv_* would be > cumbersome because we'd need a BdrvChild. As we already got the > functionality to disable request queuing from 1., use it in tests, > too, for convenience. >=20 > Signed-off-by: Kevin Wolf > --- > include/sysemu/block-backend.h | 11 +++--- > block/backup.c | 1 + > block/block-backend.c | 69 +++++++++++++++++++++++++++++-----= > block/commit.c | 2 + > block/mirror.c | 6 ++- > blockjob.c | 3 ++ > tests/test-bdrv-drain.c | 1 + > 7 files changed, 76 insertions(+), 17 deletions(-) [...] > diff --git a/block/block-backend.c b/block/block-backend.c > index fdd6b01ecf..603b281743 100644 > --- a/block/block-backend.c > +++ b/block/block-backend.c [...] > @@ -1127,13 +1136,26 @@ static int blk_check_byte_request(BlockBackend = *blk, int64_t offset, > return 0; > } > =20 > +static void blk_wait_while_drained(BlockBackend *blk) +coroutine_fn? (Maybe even blk_co_wait...) > +{ > + if (blk->quiesce_counter && !blk->disable_request_queuing) { > + qemu_co_queue_wait(&blk->queued_requests, NULL); > + } > +} > + > int coroutine_fn blk_co_preadv(BlockBackend *blk, int64_t offset, > unsigned int bytes, QEMUIOVector *qiov,= > - BdrvRequestFlags flags) > + BdrvRequestFlags flags, bool wait_while= _drained) What=E2=80=99s the purpose of this parameter? How would it hurt to alway= s wait_while_drained? I see the following callers of blk_co_p{read,write}v() that call it with wait_while_drained=3Dfalse: 1. blk_aio_{read,write}_entry(): They wait themselves, so they don=E2=80=99= t need these functions to wait. But OTOH, because they have waited, we know that the BB is not quiesced here, so we won=E2=80=99t wait here a= nyway. (These functions should be coroutine_fn, too, by the way) 2. mirror: It disables request queuing anyway, so wait_while_drained doesn=E2=80=99t have any effect. > { > int ret; > - BlockDriverState *bs =3D blk_bs(blk); > + BlockDriverState *bs; > =20 > + if (wait_while_drained) { > + blk_wait_while_drained(blk); > + } [...] What about blk_co_flush()? Should that wait, too? > @@ -2232,6 +2278,9 @@ static void blk_root_drained_end(BdrvChild *child= , int *drained_end_counter) > if (blk->dev_ops && blk->dev_ops->drained_end) { > blk->dev_ops->drained_end(blk->dev_opaque); > } > + while (qemu_co_enter_next(&blk->queued_requests, NULL)) { > + /* Resume all queued requests */ > + } Wouldn=E2=80=99t qemu_co_queue_restart_all(&blk->queued_requests) achieve= the same? Max --gTLn0QrhM5vCYUwfA1TrrSnBAvpm7K3qL-- --MIUOMaStJrWWWO8m9kX8NBy4lzGxV7mKQ Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl062voACgkQ9AfbAGHV z0DjJwf/RzoPjWMv2PlTfdYGEj0ksKygzIX633jqst/PEKJB8NQruQqGoMz2FwHd 8Bn1U4vgNTMeqYoEh/7zgAOZO6yHfUsUkt5nd25EP9mVLuiv5v2BTWVs8RhvXorG yaXZBQ7A9rli4nri0HCX+L9RZ4twcM3gIgPKcDyVoTffItFA1JOqvm2Bq46BJH78 /yC89XoEGvg9mJkeCNn/lnr9UmP10Wa+ZMGIGL0aK6yr8NX1XaPSpsyawdv4Nskm LEapmCBL/ax8M7xviguYDjx1mWRvBUMYEAFD8pdiGQlkF25gnAD9uWRZ2OhDc1RE /vYlZYiHVBB4hgQZIIz4Z+Z06+I3lQ== =rlyL -----END PGP SIGNATURE----- --MIUOMaStJrWWWO8m9kX8NBy4lzGxV7mKQ--