linux-kernel - Re: VolanoMark regression with 2.6.27-rc1

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Date:	Mon, 04 Aug 2008 08:54:26 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Dhaval Giani <dhaval@...ux.vnet.ibm.com>
Cc:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Aneesh Kumar KV <aneesh.kumar@...ux.vnet.ibm.com>,
	Balbir Singh <balbir@...ibm.com>
Subject: Re: VolanoMark regression with 2.6.27-rc1

On Mon, 2008-08-04 at 11:23 +0530, Dhaval Giani wrote:

> Peter, vatsa, any ideas?

---
Subject: sched: scale sysctl_sched_shares_ratelimit with nr_cpus

David reported that his Niagra spend a little too much time in
tg_shares_up(), which considering he has a large cpu count makes sense.

So scale the ratelimit value with the number of cpus like we do for
other controls as well.

Reported-by: David Miller <davem@...emloft.net>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
diff --git a/kernel/sched.c b/kernel/sched.c
index 9a76e92..7eddaea 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -809,9 +809,9 @@ const_debug unsigned int sysctl_sched_nr_migrate = 32;
 
 /*
  * ratelimit for updating the group shares.
- * default: 0.5ms
+ * default: 0.25ms
  */
-const_debug unsigned int sysctl_sched_shares_ratelimit = 500000;
+const_debug unsigned int sysctl_sched_shares_ratelimit = 250000;
 
 /*
  * period over which we measure -rt task cpu usage in us.
@@ -5732,6 +5732,8 @@ static inline void sched_init_granularity(void)
 		sysctl_sched_latency = limit;
 
 	sysctl_sched_wakeup_granularity *= factor;
+
+	sysctl_sched_shares_ratelimit *= factor;
 }
 
 #ifdef CONFIG_SMP


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