[dpdk-stable] [PATCH v5] vhost_user: protect active rings from async ring changes
Maxime Coquelin
maxime.coquelin at redhat.com
Wed Jan 17 18:14:31 CET 2018
On 01/17/2018 02:49 PM, Victor Kaplansky wrote:
> When performing live migration or memory hot-plugging,
> the changes to the device and vrings made by message handler
> done independently from vring usage by PMD threads.
>
> This causes for example segfaults during live-migration
> with MQ enable, but in general virtually any request
> sent by qemu changing the state of device can cause
> problems.
>
> These patches fixes all above issues by adding a spinlock
> to every vring and requiring message handler to start operation
> only after ensuring that all PMD threads related to the device
> are out of critical section accessing the vring data.
>
> Each vring has its own lock in order to not create contention
> between PMD threads of different vrings and to prevent
> performance degradation by scaling queue pair number.
>
> See https://bugzilla.redhat.com/show_bug.cgi?id=1450680
>
> Signed-off-by: Victor Kaplansky <victork at redhat.com>
> ---
> v5:
> o get rid of spinlock wrapping functions in vhost.h
>
> v4:
>
> o moved access_unlock before accessing enable flag and
> access_unlock after iommu_unlock consistently.
> o cosmetics: removed blank line.
> o the access_lock variable moved to be in the same
> cache line with enable and access_ok flags.
> o dequeue path is now guarded with trylock and returning
> zero if unsuccessful.
> o GET_VRING_BASE operation is not guarded by access lock
> to avoid deadlock with device_destroy. See the comment
> in the code.
> o Fixed error path exit from enqueue and dequeue carefully
> unlocking access and iommu locks as appropriate.
>
> v3:
> o Added locking to enqueue flow.
> o Enqueue path guarded as well as dequeue path.
> o Changed name of active_lock.
> o Added initialization of guarding spinlock.
> o Reworked functions skimming over all virt-queues.
> o Performance measurements done by Maxime Coquelin shows
> no degradation in bandwidth and throughput.
> o Spelling.
> o Taking lock only on set operations.
> o IOMMU messages are not guarded by access lock.
>
> v2:
> o Fixed checkpatch complains.
> o Added Signed-off-by.
> o Refined placement of guard to exclude IOMMU messages.
> o TODO: performance degradation measurement.
>
> lib/librte_vhost/vhost.h | 6 ++--
> lib/librte_vhost/vhost.c | 1 +
> lib/librte_vhost/vhost_user.c | 70 +++++++++++++++++++++++++++++++++++++++++++
> lib/librte_vhost/virtio_net.c | 28 ++++++++++++++---
> 4 files changed, 99 insertions(+), 6 deletions(-)
>
Reviewed-by: Maxime Coquelin <maxime.coquelin at redhat.com>
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