If we are dealing with a nester percpu reader, we can optimize away quite a few costly operations. Improve that fastpath further, by avoiding the unnecessary addition and subtraction of 'READER_PRESENT' to reader_refcnt, by rearranging the code a bit. Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx> --- lib/percpu-rwlock.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) diff --git a/lib/percpu-rwlock.c b/lib/percpu-rwlock.c index ce7e440..ed36531 100644 --- a/lib/percpu-rwlock.c +++ b/lib/percpu-rwlock.c @@ -80,23 +80,21 @@ void percpu_read_lock_irqsafe(struct percpu_rwlock *pcpu_rwlock) preempt_disable(); /* - * Let the writer know that a reader is active, even before we choose - * our reader-side synchronization scheme. - */ - this_cpu_add(pcpu_rwlock->rw_state->reader_refcnt, READER_PRESENT); - - /* * If we are already using per-cpu refcounts, it is not safe to switch * the synchronization scheme. So continue using the refcounts. */ if (reader_uses_percpu_refcnt(pcpu_rwlock)) { this_cpu_inc(pcpu_rwlock->rw_state->reader_refcnt); - this_cpu_sub(pcpu_rwlock->rw_state->reader_refcnt, - READER_PRESENT); return; } /* + * Let the writer know that a reader is active, even before we choose + * our reader-side synchronization scheme. + */ + this_cpu_add(pcpu_rwlock->rw_state->reader_refcnt, READER_PRESENT); + + /* * The write to 'reader_refcnt' must be visible before we read * 'writer_signal'. */ -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html