x86/UV: Lower UV rtc clocksource rating

Lower the rating of the UV rtc clocksource to just below that of
the tsc, to improve performance.

Reading the tsc clocksource has lower latency than reading the
rtc, so favor it in situations where it is synchronized and
stable.  When the tsc is unsynchronized, the rtc needs to be the
chosen clocksource.

Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Jack Steiner <steiner@sgi.com>
Link: http://lkml.kernel.org/r/20120217141641.GA28063@sgi.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/platform/uv/uv_time.c b/arch/x86/platform/uv/uv_time.c
index 9f29a01ee1b3fec6e8d13dce479d352d8a2eae0c..5032e0d19b8670b14cda20890a80dd0b91129b25 100644 (file)
--- a/arch/x86/platform/uv/uv_time.c
+++ b/arch/x86/platform/uv/uv_time.c
@@ -37,7 +37,7 @@ static void uv_rtc_timer_setup(enum clock_event_mode,
 
 static struct clocksource clocksource_uv = {
        .name           = RTC_NAME,
-       .rating         = 400,
+       .rating         = 299,
        .read           = uv_read_rtc,
        .mask           = (cycle_t)UVH_RTC_REAL_TIME_CLOCK_MASK,
        .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
@@ -379,10 +379,6 @@ static __init int uv_rtc_setup_clock(void)
        if (!is_uv_system())
                return -ENODEV;
 
-       /* If single blade, prefer tsc */
-       if (uv_num_possible_blades() == 1)
-               clocksource_uv.rating = 250;
-
        rc = clocksource_register_hz(&clocksource_uv, sn_rtc_cycles_per_second);
        if (rc)
                printk(KERN_INFO "UV RTC clocksource failed rc %d\n", rc);