1. 27 May, 2010 3 commits
  2. 25 May, 2010 1 commit
  3. 12 May, 2010 1 commit
    • Michael S. Tsirkin's avatar
      vhost: fix barrier pairing · 0d499356
      Michael S. Tsirkin authored
      According to memory-barriers.txt, an smp memory barrier in guest
      should always be paired with an smp memory barrier in host,
      and I quote "a lack of appropriate pairing is almost certainly an
      error". In case of vhost, failure to flush out used index
      update before looking at the interrupt disable flag
      could result in missed interrupts, resulting in
      networking hang under stress.
      
      This might happen when flags read bypasses used index write.
      So we see interrupts disabled and do not interrupt, at the
      same time guest writes flags value to enable interrupt,
      reads an old used index value, thinks that
      used ring is empty and waits for interrupt.
      
      Note: the barrier we pair with here is in
      drivers/virtio/virtio_ring.c, function
      vring_enable_cb.
      Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
      Acked-by: default avatarJuan Quintela <quintela@redhat.com>
      0d499356
  4. 14 Apr, 2010 1 commit
  5. 07 Apr, 2010 1 commit
  6. 30 Mar, 2010 1 commit
    • Tejun Heo's avatar
      include cleanup: Update gfp.h and slab.h includes to prepare for breaking... · 5a0e3ad6
      Tejun Heo authored
      include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h
      
      percpu.h is included by sched.h and module.h and thus ends up being
      included when building most .c files.  percpu.h includes slab.h which
      in turn includes gfp.h making everything defined by the two files
      universally available and complicating inclusion dependencies.
      
      percpu.h -> slab.h dependency is about to be removed.  Prepare for
      this change by updating users of gfp and slab facilities include those
      headers directly instead of assuming availability.  As this conversion
      needs to touch large number of source files, the following script is
      used as the basis of conversion.
      
        http://userweb.kernel.org/~tj/misc/slabh-sweep.py
      
      The script does the followings.
      
      * Scan files for gfp and slab usages and update includes such that
        only the necessary includes are there.  ie. if only gfp is used,
        gfp.h, if slab is used, slab.h.
      
      * When the script inserts a new include, it looks at the include
        blocks and try to put the new include such that its order conforms
        to its surrounding.  It's put in the include block which contains
        core kernel includes, in the same order that the rest are ordered -
        alphabetical, Christmas tree, rev-Xmas-tree or at the end if there
        doesn't seem to be any matching order.
      
      * If the script can't find a place to put a new include (mostly
        because the file doesn't have fitting include block), it prints out
        an error message indicating which .h file needs to be added to the
        file.
      
      The conversion was done in the following steps.
      
      1. The initial automatic conversion of all .c files updated slightly
         over 4000 files, deleting around 700 includes and adding ~480 gfp.h
         and ~3000 slab.h inclusions.  The script emitted errors for ~400
         files.
      
      2. Each error was manually checked.  Some didn't need the inclusion,
         some needed manual addition while adding it to implementation .h or
         embedding .c file was more appropriate for others.  This step added
         inclusions to around 150 files.
      
      3. The script was run again and the output was compared to the edits
         from #2 to make sure no file was left behind.
      
      4. Several build tests were done and a couple of problems were fixed.
         e.g. lib/decompress_*.c used malloc/free() wrappers around slab
         APIs requiring slab.h to be added manually.
      
      5. The script was run on all .h files but without automatically
         editing them as sprinkling gfp.h and slab.h inclusions around .h
         files could easily lead to inclusion dependency hell.  Most gfp.h
         inclusion directives were ignored as stuff from gfp.h was usually
         wildly available and often used in preprocessor macros.  Each
         slab.h inclusion directive was examined and added manually as
         necessary.
      
      6. percpu.h was updated not to include slab.h.
      
      7. Build test were done on the following configurations and failures
         were fixed.  CONFIG_GCOV_KERNEL was turned off for all tests (as my
         distributed build env didn't work with gcov compiles) and a few
         more options had to be turned off depending on archs to make things
         build (like ipr on powerpc/64 which failed due to missing writeq).
      
         * x86 and x86_64 UP and SMP allmodconfig and a custom test config.
         * powerpc and powerpc64 SMP allmodconfig
         * sparc and sparc64 SMP allmodconfig
         * ia64 SMP allmodconfig
         * s390 SMP allmodconfig
         * alpha SMP allmodconfig
         * um on x86_64 SMP allmodconfig
      
      8. percpu.h modifications were reverted so that it could be applied as
         a separate patch and serve as bisection point.
      
      Given the fact that I had only a couple of failures from tests on step
      6, I'm fairly confident about the coverage of this conversion patch.
      If there is a breakage, it's likely to be something in one of the arch
      headers which should be easily discoverable easily on most builds of
      the specific arch.
      Signed-off-by: default avatarTejun Heo <tj@kernel.org>
      Guess-its-ok-by: default avatarChristoph Lameter <cl@linux-foundation.org>
      Cc: Ingo Molnar <mingo@redhat.com>
      Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
      5a0e3ad6
  7. 17 Mar, 2010 1 commit
  8. 28 Feb, 2010 3 commits
  9. 15 Feb, 2010 1 commit
  10. 15 Jan, 2010 1 commit
    • Michael S. Tsirkin's avatar
      vhost_net: a kernel-level virtio server · 3a4d5c94
      Michael S. Tsirkin authored
      What it is: vhost net is a character device that can be used to reduce
      the number of system calls involved in virtio networking.
      Existing virtio net code is used in the guest without modification.
      
      There's similarity with vringfd, with some differences and reduced scope
      - uses eventfd for signalling
      - structures can be moved around in memory at any time (good for
        migration, bug work-arounds in userspace)
      - write logging is supported (good for migration)
      - support memory table and not just an offset (needed for kvm)
      
      common virtio related code has been put in a separate file vhost.c and
      can be made into a separate module if/when more backends appear.  I used
      Rusty's lguest.c as the source for developing this part : this supplied
      me with witty comments I wouldn't be able to write myself.
      
      What it is not: vhost net is not a bus, and not a generic new system
      call. No assumptions are made on how guest performs hypercalls.
      Userspace hypervisors are supported as well as kvm.
      
      How it works: Basically, we connect virtio frontend (configured by
      userspace) to a backend. The backend could be a network device, or a tap
      device.  Backend is also configured by userspace, including vlan/mac
      etc.
      
      Status: This works for me, and I haven't see any crashes.
      Compared to userspace, people reported improved latency (as I save up to
      4 system calls per packet), as well as better bandwidth and CPU
      utilization.
      
      Features that I plan to look at in the future:
      - mergeable buffers
      - zero copy
      - scalability tuning: figure out the best threading model to use
      
      Note on RCU usage (this is also documented in vhost.h, near
      private_pointer which is the value protected by this variant of RCU):
      what is happening is that the rcu_dereference() is being used in a
      workqueue item.  The role of rcu_read_lock() is taken on by the start of
      execution of the workqueue item, of rcu_read_unlock() by the end of
      execution of the workqueue item, and of synchronize_rcu() by
      flush_workqueue()/flush_work(). In the future we might need to apply
      some gcc attribute or sparse annotation to the function passed to
      INIT_WORK(). Paul's ack below is for this RCU usage.
      
      (Includes fixes by Alan Cox <alan@linux.intel.com>,
      David L Stevens <dlstevens@us.ibm.com>,
      Chris Wright <chrisw@redhat.com>)
      Acked-by: default avatarRusty Russell <rusty@rustcorp.com.au>
      Acked-by: default avatarArnd Bergmann <arnd@arndb.de>
      Acked-by: default avatar"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
      Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      3a4d5c94