core: make time_wait call pollers if on boot CPU

Instead of running the pollers flat out, instead call them once every
5ms. This helps in situations where pollers are taking locks that are
also taken by tasks completing on other CPUs.

The 5ms time is arbitrary; it was chosen such that most callers of
time_wait will call the pollers at least twice.

Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 20 insertions, 4 deletions

diff --git a/core/timebase.c b/core/timebase.c
index fb46bcf4..7e3345f8 100644
--- a/core/timebase.c
+++ b/core/timebase.c
@@ -18,15 +18,31 @@
 #include <opal.h>
 #include <cpu.h>
 
-void time_wait(unsigned long duration)
+static void time_wait_poll(unsigned long duration)
 {
+	unsigned long remaining = duration;
 	unsigned long end = mftb() + duration;
+	unsigned long period = msecs_to_tb(5);
+
+	while (tb_compare(mftb(), end) != TB_AAFTERB) {
+		/* Call pollers periodically but not continually to avoid
+		 * bouncing cachelines due to lock contention. */
+		if (remaining >= period) {
+			opal_run_pollers();
+			time_wait_nopoll(period);
+			remaining -= period;
+		}
 
-	while(tb_compare(mftb(), end) != TB_AAFTERB) {
-		opal_run_pollers();
 		cpu_relax();
-        }
+	}
+}
 
+void time_wait(unsigned long duration)
+{
+	if (this_cpu() != boot_cpu)
+		time_wait_nopoll(duration);
+	else
+		time_wait_poll(duration);
 }
 
 void time_wait_nopoll(unsigned long duration)