Re: [PATCH 0/5] virtio-gpu: Force RCU when unmapping blob

["Alex Bennée" <alex.bennee@linaro.org>]

Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp> writes:

> Based-on: <20251016-force-v1-1-919a82112498@rsg.ci.i.u-tokyo.ac.jp>
> ("[PATCH] rcu: Unify force quiescent state")
>
> Unmapping a blob changes the memory map, which is protected with RCU.
> RCU is designed to minimize the read-side overhead at the cost of
> reclamation delay. While this design usually makes sense, it is
> problematic when unmapping a blob because the operation blocks all
> virtio-gpu commands and causes perceivable disruption.
>
> Minimize such the disruption with force_rcu(), which minimizes the
> reclamation delay at the cost of a read-side overhead.
>
> Dmitry, can you see if this change makes difference?

Also works with the blob test:

  ➜  ./pyvenv/bin/meson test --setup thorough func-aarch64-gpu_blob
  ninja: Entering directory `/home/alex/lsrc/qemu.git/builds/all'
  [1/6] Generating qemu-version.h with a custom command (wrapped by meson to capture output)
  1/1 qemu:func-thorough+func-aarch64-thorough+thorough / func-aarch64-gpu_blob        OK              0.37s   1 subtests passed

  Ok:                 1   
  Expected Fail:      0   
  Fail:               0   
  Unexpected Pass:    0   
  Skipped:            0   
  Timeout:            0   

  Full log written to /home/alex/lsrc/qemu.git/builds/all/meson-logs/testlog-thorough.txt
  🕙17:57:38 alex@draig:qemu.git/builds/all  on  virtio-gpu/next [$!?] 

so a Tested-by: Alex Bennée <alex.bennee@linaro.org> from me.


>
> Signed-off-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
> ---
> Akihiko Odaki (5):
>       futex: Add qemu_futex_timedwait()
>       qemu-thread: Add qemu_event_timedwait()
>       rcu: Use call_rcu() in synchronize_rcu()
>       rcu: Wake the RCU thread when draining
>       virtio-gpu: Force RCU when unmapping blob
>
>  include/qemu/futex.h          |  29 ++++++--
>  include/qemu/rcu.h            |   1 +
>  include/qemu/thread-posix.h   |  11 +++
>  include/qemu/thread.h         |   8 ++-
>  hw/display/virtio-gpu-virgl.c |   1 +
>  util/event.c                  |  34 ++++++++--
>  util/qemu-thread-posix.c      |  11 +--
>  util/rcu.c                    | 153 ++++++++++++++++++++++++------------------
>  8 files changed, 163 insertions(+), 85 deletions(-)
> ---
> base-commit: ee7fbe81705732785aef2cb568bbc5d8f7d2fce1
> change-id: 20251027-force_rcu-616c743373f7
>
> Best regards,

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro