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    SubjectRe: [PATCH 2/6] Don't touch the snap in srcu_readers_active()
    On Tue, Mar 06, 2012 at 05:57:34PM +0800, Lai Jiangshan wrote:
    > srcu_readers_active() is called without the mutex, but it touch the snap.
    > also achieve better cache locality a little
    >
    > Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>

    Queued with updated commit-log message, thank you!

    Thanx, Paul

    Expand the calls to srcu_readers_active_idx() from
    srcu_readers_active() inline. This change improves cache locality
    by interating over the CPUs once rather than twice.

    > ---
    > kernel/srcu.c | 9 ++++++++-
    > 1 files changed, 8 insertions(+), 1 deletions(-)
    >
    > diff --git a/kernel/srcu.c b/kernel/srcu.c
    > index b6b9ea2..fbe2d5f 100644
    > --- a/kernel/srcu.c
    > +++ b/kernel/srcu.c
    > @@ -181,7 +181,14 @@ static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx)
    > */
    > static int srcu_readers_active(struct srcu_struct *sp)
    > {
    > - return srcu_readers_active_idx(sp, 0) + srcu_readers_active_idx(sp, 1);
    > + int cpu;
    > + unsigned long sum = 0;
    > +
    > + for_each_possible_cpu(cpu) {
    > + sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[0]);
    > + sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[1]);
    > + }
    > + return sum & SRCU_REF_MASK;
    > }
    >
    > /**
    > --
    > 1.7.4.4
    >



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