[Qemu-devel] [PULL for-2.11-rc1 0/2] Block patches
[PULL 0/1] Block patches
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The following changes since commit b0fbe46ad82982b289a44ee2495b59b0bad8a842:
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The following changes since commit 887cba855bb6ff4775256f7968409281350b568c:
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Update version for v2.11.0-rc0 release (2017-11-07 16:05:28 +0000)
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configure: Fix cross-building for RISCV host (v5) (2023-07-11 17:56:09 +0100)
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are available in the git repository at:
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are available in the Git repository at:
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git://github.com/stefanha/qemu.git tags/block-pull-request
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https://gitlab.com/stefanha/qemu.git tags/block-pull-request
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for you to fetch changes up to 161d53bbed2be4c4336c098185de3afb13cc6bd5:
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for you to fetch changes up to 75dcb4d790bbe5327169fd72b185960ca58e2fa6:
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util/async: use atomic_mb_set in qemu_bh_cancel (2017-11-08 09:24:41 +0000)
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virtio-blk: fix host notifier issues during dataplane start/stop (2023-07-12 15:20:32 -0400)
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----------------------------------------------------------------
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Pull request
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----------------------------------------------------------------
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----------------------------------------------------------------
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----------------------------------------------------------------
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Stefan Hajnoczi (1):
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virtio-blk: fix host notifier issues during dataplane start/stop
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Sergio Lopez (1):
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hw/block/dataplane/virtio-blk.c | 67 +++++++++++++++++++--------------
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util/async: use atomic_mb_set in qemu_bh_cancel
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1 file changed, 38 insertions(+), 29 deletions(-)
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Stefan Hajnoczi (1):
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tests-aio-multithread: fix /aio/multi/schedule race condition
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tests/test-aio-multithread.c | 5 ++---
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util/async.c | 2 +-
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2 files changed, 3 insertions(+), 4 deletions(-)
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--
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--
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2.13.6
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2.40.1
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diff view generated by jsdifflib
New patch
[PULL 1/1] virtio-blk: fix host notifier issues during dataplane start/stop
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The main loop thread can consume 100% CPU when using --device
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virtio-blk-pci,iothread=<iothread>. ppoll() constantly returns but
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reading virtqueue host notifiers fails with EAGAIN. The file descriptors
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are stale and remain registered with the AioContext because of bugs in
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the virtio-blk dataplane start/stop code.
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The problem is that the dataplane start/stop code involves drain
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operations, which call virtio_blk_drained_begin() and
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virtio_blk_drained_end() at points where the host notifier is not
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operational:
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- In virtio_blk_data_plane_start(), blk_set_aio_context() drains after
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vblk->dataplane_started has been set to true but the host notifier has
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not been attached yet.
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- In virtio_blk_data_plane_stop(), blk_drain() and blk_set_aio_context()
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drain after the host notifier has already been detached but with
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vblk->dataplane_started still set to true.
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I would like to simplify ->ioeventfd_start/stop() to avoid interactions
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with drain entirely, but couldn't find a way to do that. Instead, this
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patch accepts the fragile nature of the code and reorders it so that
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vblk->dataplane_started is false during drain operations. This way the
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virtio_blk_drained_begin() and virtio_blk_drained_end() calls don't
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touch the host notifier. The result is that
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virtio_blk_data_plane_start() and virtio_blk_data_plane_stop() have
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complete control over the host notifier and stale file descriptors are
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no longer left in the AioContext.
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This patch fixes the 100% CPU consumption in the main loop thread and
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correctly moves host notifier processing to the IOThread.
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Fixes: 1665d9326fd2 ("virtio-blk: implement BlockDevOps->drained_begin()")
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Reported-by: Lukáš Doktor <ldoktor@redhat.com>
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Tested-by: Lukas Doktor <ldoktor@redhat.com>
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Message-id: 20230704151527.193586-1-stefanha@redhat.com
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Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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---
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hw/block/dataplane/virtio-blk.c | 67 +++++++++++++++++++--------------
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1 file changed, 38 insertions(+), 29 deletions(-)
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diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
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index XXXXXXX..XXXXXXX 100644
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--- a/hw/block/dataplane/virtio-blk.c
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+++ b/hw/block/dataplane/virtio-blk.c
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@@ -XXX,XX +XXX,XX @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
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memory_region_transaction_commit();
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- /*
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- * These fields are visible to the IOThread so we rely on implicit barriers
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- * in aio_context_acquire() on the write side and aio_notify_accept() on
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- * the read side.
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- */
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- s->starting = false;
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- vblk->dataplane_started = true;
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trace_virtio_blk_data_plane_start(s);
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old_context = blk_get_aio_context(s->conf->conf.blk);
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@@ -XXX,XX +XXX,XX @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
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event_notifier_set(virtio_queue_get_host_notifier(vq));
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}
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+ /*
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+ * These fields must be visible to the IOThread when it processes the
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+ * virtqueue, otherwise it will think dataplane has not started yet.
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+ *
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+ * Make sure ->dataplane_started is false when blk_set_aio_context() is
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+ * called above so that draining does not cause the host notifier to be
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+ * detached/attached prematurely.
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+ */
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+ s->starting = false;
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+ vblk->dataplane_started = true;
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+ smp_wmb(); /* paired with aio_notify_accept() on the read side */
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+
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/* Get this show started by hooking up our callbacks */
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if (!blk_in_drain(s->conf->conf.blk)) {
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aio_context_acquire(s->ctx);
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@@ -XXX,XX +XXX,XX @@ int virtio_blk_data_plane_start(VirtIODevice *vdev)
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fail_guest_notifiers:
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vblk->dataplane_disabled = true;
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s->starting = false;
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- vblk->dataplane_started = true;
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return -ENOSYS;
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}
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@@ -XXX,XX +XXX,XX @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)
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aio_wait_bh_oneshot(s->ctx, virtio_blk_data_plane_stop_bh, s);
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}
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+ /*
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+ * Batch all the host notifiers in a single transaction to avoid
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+ * quadratic time complexity in address_space_update_ioeventfds().
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+ */
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+ memory_region_transaction_begin();
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+
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+ for (i = 0; i < nvqs; i++) {
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+ virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), i, false);
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+ }
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+
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+ /*
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+ * The transaction expects the ioeventfds to be open when it
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+ * commits. Do it now, before the cleanup loop.
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+ */
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+ memory_region_transaction_commit();
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+
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+ for (i = 0; i < nvqs; i++) {
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+ virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), i);
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+ }
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+
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+ /*
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+ * Set ->dataplane_started to false before draining so that host notifiers
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+ * are not detached/attached anymore.
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+ */
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+ vblk->dataplane_started = false;
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+
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aio_context_acquire(s->ctx);
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/* Wait for virtio_blk_dma_restart_bh() and in flight I/O to complete */
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@@ -XXX,XX +XXX,XX @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev)
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aio_context_release(s->ctx);
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- /*
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- * Batch all the host notifiers in a single transaction to avoid
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- * quadratic time complexity in address_space_update_ioeventfds().
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- */
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- memory_region_transaction_begin();
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-
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- for (i = 0; i < nvqs; i++) {
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- virtio_bus_set_host_notifier(VIRTIO_BUS(qbus), i, false);
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- }
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-
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- /*
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- * The transaction expects the ioeventfds to be open when it
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- * commits. Do it now, before the cleanup loop.
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- */
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- memory_region_transaction_commit();
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-
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- for (i = 0; i < nvqs; i++) {
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- virtio_bus_cleanup_host_notifier(VIRTIO_BUS(qbus), i);
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- }
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-
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qemu_bh_cancel(s->bh);
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notify_guest_bh(s); /* final chance to notify guest */
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/* Clean up guest notifier (irq) */
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k->set_guest_notifiers(qbus->parent, nvqs, false);
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- vblk->dataplane_started = false;
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s->stopping = false;
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}
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--
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2.40.1
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diff view generated by jsdifflib

Patchew 2.1-devel-b67e4c2

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