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Message-Id: <200711181120.27459.mitov@issp.bas.bg>
Date: Sun, 18 Nov 2007 11:20:27 +0200
From: Marin Mitov <mitov@...p.bas.bg>
To: linux-kernel@...r.kernel.org
Subject: [PATCH]new_TSC_based_delay_tsc()
Hi all,
This is a patch based on the Ingo's idea/patch to track
delay_tsc() migration to another cpu by comparing
smp_processor_id(). It is against kernel-2.6.24-rc3.
What is different:
1. Using unsigned (instead of long) to unify for i386/x86_64.
2. Minimal preempt_disable/enable() critical sections
(more room for preemption)
3. some statements have been rearranged, to account for
possible under/overflow of left/TSC
Tested on both: 32/64 bit SMP PREEMPT kernel-2.6.24-rc3
Hope it is correct. Comments, please.
Signed-off-by: Marin Mitov <mitov@...p.bas.bg>
=========================================
--- a/arch/x86/lib/delay_32.c 2007-11-18 10:20:45.000000000 +0200
+++ b/arch/x86/lib/delay_32.c 2007-11-18 10:20:44.000000000 +0200
@@ -38,18 +38,41 @@
:"0" (loops));
}
-/* TSC based delay: */
+/* TSC based delay:
+ *
+ * We are careful about preemption as TSC's are per-CPU.
+ */
static void delay_tsc(unsigned long loops)
{
- unsigned long bclock, now;
+ unsigned prev, now;
+ unsigned left = loops;
+ unsigned prev_cpu, cpu;
+
+ preempt_disable();
+ rdtscl(prev);
+ prev_cpu = smp_processor_id();
+ preempt_enable();
+ now = prev;
- preempt_disable(); /* TSC's are per-cpu */
- rdtscl(bclock);
do {
rep_nop();
+
+ left -= now - prev;
+ prev = now;
+
+ preempt_disable();
rdtscl(now);
- } while ((now-bclock) < loops);
- preempt_enable();
+ cpu = smp_processor_id();
+ preempt_enable();
+
+ if (prev_cpu != cpu){
+ /*
+ * We have migrated, we skip this small amount of time:
+ */
+ prev = now;
+ prev_cpu = cpu;
+ }
+ } while ((now-prev) < left);
}
/*
--- a/arch/x86/lib/delay_64.c 2007-11-18 10:20:44.000000000 +0200
+++ b/arch/x86/lib/delay_64.c 2007-11-18 10:20:44.000000000 +0200
@@ -26,18 +26,42 @@
return 0;
}
+/* TSC based delay:
+ *
+ * We are careful about preemption as TSC's are per-CPU.
+ */
void __delay(unsigned long loops)
{
- unsigned bclock, now;
+ unsigned prev, now;
+ unsigned left = loops;
+ unsigned prev_cpu, cpu;
+
+ preempt_disable();
+ rdtscl(prev);
+ prev_cpu = smp_processor_id();
+ preempt_enable();
+ now = prev;
- preempt_disable(); /* TSC's are pre-cpu */
- rdtscl(bclock);
do {
- rep_nop();
+ rep_nop();
+
+ left -= now - prev;
+ prev = now;
+
+ preempt_disable();
rdtscl(now);
+ cpu = smp_processor_id();
+ preempt_enable();
+
+ if (prev_cpu != cpu){
+ /*
+ * We have migrated, we skip this small amount of time:
+ */
+ prev = now;
+ prev_cpu = cpu;
+ }
}
- while ((now-bclock) < loops);
- preempt_enable();
+ while ((now-prev) < left);
}
EXPORT_SYMBOL(__delay);
-
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