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SubjectRe: [PATCH] Inline double_unlock_balance()
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On Wed, 2008-11-05 at 18:57 +0530, Sripathi Kodi wrote:
> Hi,
>
> We have a test case which measures the variation in the amount of time
> needed to perform a fixed amount of work on the preempt_rt kernel. We
> started seeing deterioration in it's performance recently. The test
> should never take more than 10 microseconds, but we started 5-10%
> failure rate. Using elimination method, we traced the problem to commit
> 1b12bbc747560ea68bcc132c3d05699e52271da0 (lockdep: re-annotate
> scheduler runqueues). When LOCKDEP is disabled, this patch only adds an
> additional function call to double_unlock_balance(). Hence I inlined
> double_unlock_balance() and the problem went away. Here is a patch to
> make this change.
>
> Thanks,
> Sripathi.
>
> lockdep: Inline double_unlock_balance()
>
> Additional function call for double_unlock_balance() causes latency
> problems for some test cases on the preempt_rt kernel.
>
> Signed-off-by: Sripathi Kodi <sripathik@in.ibm.com>

Acked-by; Peter Zijlstra <a.p.zijlstra@chello.nl>

> Index: linux-2.6.27.4/kernel/sched.c
> ===================================================================
> --- linux-2.6.27.4.orig/kernel/sched.c 2008-11-05 05:01:01.000000000 -0800
> +++ linux-2.6.27.4/kernel/sched.c 2008-11-05 05:01:20.000000000 -0800
> @@ -2812,7 +2812,7 @@
> return ret;
> }
>
> -static void double_unlock_balance(struct rq *this_rq, struct rq *busiest)
> +static inline void double_unlock_balance(struct rq *this_rq, struct rq *busiest)
> __releases(busiest->lock)
> {
> spin_unlock(&busiest->lock);



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