Re: [PATCH] Inline double_unlock_balance()

[Peter Zijlstra]

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@xxxxxxxxxx>

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

> 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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