Merge commit '900cfa46191a7d87cf1891924cb90499287fd235'; branches 'timers/nohz',...

[cascardo/linux.git] / arch / x86 / lib / delay_32.c

diff --git a/arch/x86/lib/delay_32.c b/arch/x86/lib/delay_32.c
index 4535e6d..d710f2d 100644 (file)
--- a/arch/x86/lib/delay_32.c
+++ b/arch/x86/lib/delay_32.c
@@ -44,13 +44,36 @@ static void delay_loop(unsigned long loops)
 static void delay_tsc(unsigned long loops)
 {
        unsigned long bclock, now;
+       int cpu;
 
-       preempt_disable();              /* TSC's are per-cpu */
+       preempt_disable();
+       cpu = smp_processor_id();
        rdtscl(bclock);
-       do {
-               rep_nop();
+       for (;;) {
                rdtscl(now);
-       } while ((now-bclock) < loops);
+               if ((now - bclock) >= loops)
+                       break;
+
+               /* Allow RT tasks to run */
+               preempt_enable();
+               rep_nop();
+               preempt_disable();
+
+               /*
+                * It is possible that we moved to another CPU, and
+                * since TSC's are per-cpu we need to calculate
+                * that. The delay must guarantee that we wait "at
+                * least" the amount of time. Being moved to another
+                * CPU could make the wait longer but we just need to
+                * make sure we waited long enough. Rebalance the
+                * counter for this CPU.
+                */
+               if (unlikely(cpu != smp_processor_id())) {
+                       loops -= (now - bclock);
+                       cpu = smp_processor_id();
+                       rdtscl(bclock);
+               }
+       }
        preempt_enable();
 }