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    SubjectRe: [patch 2/4] lglock: introduce special lglock and brlock spin locks
    On Fri, Jun 04, 2010 at 09:56:03AM +0200, Eric Dumazet wrote:
    > Le vendredi 04 juin 2010 à 16:43 +1000, Nick Piggin a écrit :
    > > pièce jointe document texte brut (kernel-introduce-brlock.patch)
    > > This patch introduces "local-global" locks (lglocks). These can be used to:
    > >
    > > - Provide fast exclusive access to per-CPU data, with exclusive access to
    > > another CPU's data allowed but possibly subject to contention, and to provide
    > > very slow exclusive access to all per-CPU data.
    > > - Or to provide very fast and scalable read serialisation, and to provide
    > > very slow exclusive serialisation of data (not necessarily per-CPU data).
    > >
    > > Brlocks are also implemented as a short-hand notation for the latter use
    > > case.
    > >
    > > Thanks to Paul for local/global naming convention.
    > >
    > > Cc: linux-kernel@vger.kernel.org
    > > Cc: linux-fsdevel@vger.kernel.org
    > > Cc: Al Viro <viro@ZenIV.linux.org.uk>
    > > Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
    > > Cc: Frank Mayhar <fmayhar@google.com>,
    > > Cc: John Stultz <johnstul@us.ibm.com>
    > > Cc: Andi Kleen <ak@linux.intel.com>
    > > Signed-off-by: Nick Piggin <npiggin@suse.de>
    > > ---
    > > include/linux/lglock.h | 165 +++++++++++++++++++++++++++++++++++++++++++++++++
    > > 1 file changed, 165 insertions(+)
    > >
    >
    > IMHO some changes in Documentation/ would be needed

    I wonder where, and what?


    > > + void name##_global_lock(void) { \
    > > + int i; \
    > > + preempt_disable(); \
    > > + rwlock_acquire(&name##_lock_dep_map, 0, 0, _RET_IP_); \
    > > + for_each_online_cpu(i) { \
    >
    > for_each_possible_cpu()

    Oh good spotting. brlock does not need this but lglock does if it
    protects offline cpu data too. Maybe better to move file handles in
    the event of hotplug.

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