[PATCH] x86/apic: Don't use the tsc in setup_local_APIC

[Eric W . Biederman]

If everything is initialized in the order of init/main.c we should have:
init_IRQ()
    setup_local_APIC()
time_init()
    tsc_init()
local_irq_enable()

Which means the only reason the current use of the tsc in setup_local_APIC
works is because we are calling setup_local_APIC late on most x86
platforms.

The justification given for using a 1 second timeout on this loop
is because virtualized platforms have a very expensive apic_read().

Typically this loop should execute exactly once after confirming there
is nothing to do.  On a bad day this loop should execute twice
after clearing the ISR and the IRR unacked irqs.  If it is too
expensive to execute this loop twice on a virtualized platform
that is not our problem.

Let's set max_loops to 5.  Which is more than enough and that
removes the need for messing with the tsc.

Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
---
 arch/x86/kernel/apic/apic.c |   13 ++-----------
 1 files changed, 2 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index c02cc69..d1a2b19 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -51,7 +51,6 @@
 #include <asm/smp.h>
 #include <asm/mce.h>
 #include <asm/kvm_para.h>
-#include <asm/tsc.h>
 
 unsigned int num_processors;
 
@@ -1154,11 +1153,7 @@ void __cpuinit setup_local_APIC(void)
 {
 	unsigned int value, queued;
 	int i, j, acked = 0;
-	unsigned long long tsc = 0, ntsc;
-	long long max_loops = cpu_khz;
-
-	if (cpu_has_tsc)
-		rdtscll(tsc);
+	int max_loops = 5;
 
 	if (disable_apic) {
 		arch_disable_smp_support();
@@ -1229,11 +1224,7 @@ void __cpuinit setup_local_APIC(void)
 			       acked);
 			break;
 		}
-		if (cpu_has_tsc) {
-			rdtscll(ntsc);
-			max_loops = (cpu_khz << 10) - (ntsc - tsc);
-		} else
-			max_loops--;
+		max_loops--;
 	} while (queued && max_loops > 0);
 	WARN_ON(max_loops <= 0);
 
-- 
1.6.5.2.143.g8cc62

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