linux-kernel - [RFD PATCH 1/4] powerpc: cpu: Reduce the polling interval in __cpu

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Message-ID: <20090616053844.30891.79173.stgit@sofia.in.ibm.com>
Date:	Tue, 16 Jun 2009 11:08:44 +0530
From:	Gautham R Shenoy <ego@...ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Balbir Singh <balbir@...ibm.com>,
	Rusty Russel <rusty@...tcorp.com.au>,
	Paul E McKenney <paulmck@...ibm.com>,
	Nathan Lynch <ntl@...ox.com>, Ingo Molnar <mingo@...e.hu>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Shoahua Li <shaohua.li@...ux.com>
Subject: [RFD PATCH 1/4] powerpc: cpu: Reduce the polling interval in
	__cpu_up()

The cpu online operation on a powerpc today takes order of 200-220ms. Of
this time, approximately 200ms is taken up by __cpu_up(). This is because
we poll every 200ms to check if the new cpu has notified it's presence
through the cpu_callin_map. We poll every 200ms until the new cpu sets
the value in cpu_callin_map or 5 seconds elapse, whichever comes earlier.

However, the time taken by the new processor to indicate it's presence has
found to be less than a millisecond. Keeping this in mind, reduce the
polling interval from 200ms to 1ms while retaining the 5 second timeout.

Signed-off-by: Gautham R Shenoy <ego@...ibm.com>
---
 arch/powerpc/kernel/smp.c |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 65484b2..00c13a1 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -411,9 +411,8 @@ int __cpuinit __cpu_up(unsigned int cpu)
 		 * CPUs can take much longer to come up in the
 		 * hotplug case.  Wait five seconds.
 		 */
-		for (c = 25; c && !cpu_callin_map[cpu]; c--) {
-			msleep(200);
-		}
+		for (c = 5000; c && !cpu_callin_map[cpu]; c--)
+			msleep(1);
 #endif
 
 	if (!cpu_callin_map[cpu]) {

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