[PATCH v4 0/3] xen: optimize xenbus performance

[Juergen Gross]

The xenbus driver used for communication with Xenstore (all kernel
accesses to Xenstore and in case of Xenstore living in another domain
all accesses of the local domain to Xenstore) is rather simple
especially regarding multiple concurrent accesses: they are just being
serialized in spite of Xenstore being capable to handle multiple
parallel accesses.

Clean up the external interface(s) of xenbus and optimize its
performance by allowing multiple concurrent accesses to Xenstore.

V4:
- patch 3: correct xs_request_enter()
- patch 3: correct xs_request_exit() as requested by Boris Ostrovsky

V3:
- patch 3: simplify coding as requested by Boris Ostrovsky

V2:
- patch 1: update commit message, re-add lost copyright
- patch 3: address comments of Boris Ostrovsky:
    - guard xs_request_id by lock
    - move state struct definitions to the place where they are being
      used
    - rate limit some warnings
    - use barrier() instead of cpu_relax()
    - add/remove some comments
    - minor changes like naming of variables

Juergen Gross (3):
  xen: clean up xenbus internal headers
  xen: modify xenstore watch event interface
  xen: optimize xenbus driver for multiple concurrent xenstore accesses

 drivers/block/xen-blkback/xenbus.c         |   6 +-
 drivers/net/xen-netback/xenbus.c           |   8 +-
 drivers/xen/cpu_hotplug.c                  |   5 +-
 drivers/xen/manage.c                       |   6 +-
 drivers/xen/xen-balloon.c                  |   2 +-
 drivers/xen/xen-pciback/xenbus.c           |   2 +-
 drivers/xen/xenbus/xenbus.h                | 135 +++++++
 drivers/xen/xenbus/xenbus_client.c         |   6 +-
 drivers/xen/xenbus/xenbus_comms.c          | 315 +++++++++++++++--
 drivers/xen/xenbus/xenbus_comms.h          |  51 ---
 drivers/xen/xenbus/xenbus_dev_backend.c    |   2 +-
 drivers/xen/xenbus/xenbus_dev_frontend.c   | 213 ++++++-----
 drivers/xen/xenbus/xenbus_probe.c          |  14 +-
 drivers/xen/xenbus/xenbus_probe.h          |  88 -----
 drivers/xen/xenbus/xenbus_probe_backend.c  |  11 +-
 drivers/xen/xenbus/xenbus_probe_frontend.c |  17 +-
 drivers/xen/xenbus/xenbus_xs.c             | 544 +++++++++++++----------------
 drivers/xen/xenfs/super.c                  |   2 +-
 drivers/xen/xenfs/xenstored.c              |   2 +-
 include/xen/xenbus.h                       |  18 +-
 20 files changed, 835 insertions(+), 612 deletions(-)
 create mode 100644 drivers/xen/xenbus/xenbus.h
 delete mode 100644 drivers/xen/xenbus/xenbus_comms.h
 delete mode 100644 drivers/xen/xenbus/xenbus_probe.h

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2.10.2