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| author |   John Stultz <johnstul@us.ibm.com> | 2008-08-20 16:37:28 -0700 |
|---|---|---|
| committer |   Ingo Molnar <mingo@elte.hu> | 2008-08-21 09:50:23 +0200 |
| commit | 1aa5dfb751d275ae7117d3b73ac423b4a46f2a73 (patch) | |
| tree | dde8d56d000c7885c43df0e61f72f4a75d5759fe /kernel/time | |
| parent | clocksource: check range (diff) | |
| download | linux-dev-1aa5dfb751d275ae7117d3b73ac423b4a46f2a73.tar.xz linux-dev-1aa5dfb751d275ae7117d3b73ac423b4a46f2a73.zip | |
clocksource: keep track of original clocksource frequency
The clocksource frequency is represented by
clocksource->mult/2^(clocksource->shift). Currently, when NTP makes
adjustments to the clock frequency, they are made directly to the mult
value.
This has the drawback that once changed, we cannot know what the orignal
mult value was, or how much adjustment has been applied.
This property causes problems in calculating proper ntp intervals when
switching back and forth between clocksources.
This patch separates the current mult value into a mult and mult_orig
pair. The mult_orig value stays constant, while the ntp clocksource
adjustments are done only to the mult value.
This allows for correct ntp interval calculation and additionally lays the
groundwork for a new notion of time, what I'm calling the monotonic-raw
time, which is introduced in a following patch.
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/time')
| -rw-r--r-- | kernel/time/clocksource.c | 3 | ||||
| -rw-r--r-- | kernel/time/jiffies.c | 1 |
2 files changed, 4 insertions, 0 deletions
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 093d4acf993b..9ed2eec97526 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -325,6 +325,9 @@ int clocksource_register(struct clocksource *c) unsigned long flags; int ret; + /* save mult_orig on registration */ + c->mult_orig = c->mult; + spin_lock_irqsave(&clocksource_lock, flags); ret = clocksource_enqueue(c); if (!ret) diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c index 4c256fdb8875..1ca99557e929 100644 --- a/kernel/time/jiffies.c +++ b/kernel/time/jiffies.c @@ -61,6 +61,7 @@ struct clocksource clocksource_jiffies = { .read = jiffies_read, .mask = 0xffffffff, /*32bits*/ .mult = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */ + .mult_orig = NSEC_PER_JIFFY << JIFFIES_SHIFT, .shift = JIFFIES_SHIFT, }; |