linux-kernel - [RFC patch] Use IPI_shortcut for lapic timer broadcast

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Date:	Mon, 29 Jun 2009 14:47:57 +0800
From:	Luming Yu <luming.yu@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	suresh.b.siddha@...el.com, venkatesh.pallipadi@...el.com
Subject: [RFC patch] Use IPI_shortcut for lapic timer broadcast

Hello,

We need to use IPI shortcut to send lapic timer broadcast
to avoid the latency of sending IPI one bye one on systems with many
logical processors when NO_HZ is disabled.
Without this patch,I have seen upstream kernel with RHEL 5 kernel
config boot hang .

The patch also changes physflat_send_IPI_all to IPI shortcut mode.

Please review, and apply.

**The patch is enclosed in text attachment*
**Using web client to send the patch* *
**below is for review, please apply attached  patch*/

Thanks,
Luming


Signed-off-by: Yu Luming <luming.yu@...el.com>

 apic.c         |    4 +++-
 apic_flat_64.c |    7 ++++++-
 2 files changed, 9 insertions(+), 2 deletions(-)

--- linux-2.6.30-rc6/arch/x86/kernel/apic/apic.c.0	2009-06-28
20:22:55.000000000 -0600
+++ linux-2.6.30-rc6/arch/x86/kernel/apic/apic.c	2009-06-29
00:21:44.000000000 -0600
@@ -419,7 +419,9 @@
 static void lapic_timer_broadcast(const struct cpumask *mask)
 {
 #ifdef CONFIG_SMP
-	apic->send_IPI_mask(mask, LOCAL_TIMER_VECTOR);
+	if (cpus_empty(*mask))
+		return;
+	apic->send_IPI_all(LOCAL_TIMER_VECTOR);
 #endif
 }

--- linux-2.6.30-rc6/arch/x86/kernel/apic/apic_flat_64.c.0	2009-06-29
00:13:26.000000000 -0600
+++ linux-2.6.30-rc6/arch/x86/kernel/apic/apic_flat_64.c	2009-06-29
00:11:23.000000000 -0600
@@ -274,7 +274,12 @@

 static void physflat_send_IPI_all(int vector)
 {
-	physflat_send_IPI_mask(cpu_online_mask, vector);
+	if (vector == NMI_VECTOR) {
+		physflat_send_IPI_mask(cpu_online_mask, vector);
+	} else {
+		__default_send_IPI_shortcut(APIC_DEST_ALLINC,
+					    vector, apic->dest_logical);
+	}
 }

 static unsigned int physflat_cpu_mask_to_apicid(const struct cpumask *cpumask)

Download attachment "1.patch" of type "application/octet-stream" (999 bytes)