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SubjectRe: [PATCH] x86 uv: lower UV rtc clocksource rating
On Fri, Feb 17, 2012 at 01:02:42PM +0100, Ingo Molnar wrote:
>
> * Dimitri Sivanich <sivanich@sgi.com> wrote:
>
> > Lower the rating of the UV rtc clocksource to just below that of the tsc.
>
> This changelog is deficient for obvious reasons, mind updating
> it?
>
OK. Is this sufficient?


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

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>
---
arch/x86/platform/uv/uv_time.c | 6 +-----
1 file changed, 1 insertion(+), 5 deletions(-)

Index: linux/arch/x86/platform/uv/uv_time.c
===================================================================
--- linux.orig/arch/x86/platform/uv/uv_time.c
+++ linux/arch/x86/platform/uv/uv_time.c
@@ -37,7 +37,7 @@ static void uv_rtc_timer_setup(enum cloc

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(voi
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);

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