1. 25 2月, 2009 1 次提交
    • N
      generic IPI: simplify barriers and locking · 15d0d3b3
      Nick Piggin 提交于
      Simplify the barriers in generic remote function call interrupt
      code.
      
      Firstly, just unconditionally take the lock and check the list
      in the generic_call_function_single_interrupt IPI handler. As
      we've just taken an IPI here, the chances are fairly high that
      there will be work on the list for us, so do the locking
      unconditionally. This removes the tricky lockless list_empty
      check and dubious barriers. The change looks bigger than it is
      because it is just removing an outer loop.
      
      Secondly, clarify architecture specific IPI locking rules.
      Generic code has no tools to impose any sane ordering on IPIs if
      they go outside normal cache coherency, ergo the arch code must
      make them appear to obey cache coherency as a "memory operation"
      to initiate an IPI, and a "memory operation" to receive one.
      This way at least they can be reasoned about in generic code,
      and smp_mb used to provide ordering.
      
      The combination of these two changes means that explict barriers
      can be taken out of queue handling for the single case -- shared
      data is explicitly locked, and ipi ordering must conform to
      that, so no barriers needed. An extra barrier is needed in the
      many handler, so as to ensure we load the list element after the
      IPI is received.
      
      Does any architecture actually *need* these barriers? For the
      initiator I could see it, but for the handler I would be
      surprised. So the other thing we could do for simplicity is just
      to require that, rather than just matching with cache coherency,
      we just require a full barrier before generating an IPI, and
      after receiving an IPI. In which case, the smp_mb()s can go
      away. But just for now, we'll be on the safe side and use the
      barriers (they're in the slow case anyway).
      Signed-off-by: NNick Piggin <npiggin@suse.de>
      Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
      Cc: linux-arch@vger.kernel.org
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Jens Axboe <jens.axboe@oracle.com>
      Cc: Oleg Nesterov <oleg@redhat.com>
      Cc: Suresh Siddha <suresh.b.siddha@intel.com>
      Signed-off-by: NIngo Molnar <mingo@elte.hu>
      15d0d3b3
  2. 24 2月, 2009 8 次提交
  3. 23 2月, 2009 21 次提交
  4. 22 2月, 2009 10 次提交