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Subject[RFC patch] Use IPI_shortcut for lapic timer broadcast
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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@intel.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)[unhandled content-type:application/octet-stream]
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