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ia64: Update fsyscall gettime to use modern vsyscall_update

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John Stultz provided the outline for this patch back in May 2014 here:

	http://patches.linaro.org/patch/30501/

but I let this sit on the shelf for too long and in the intervening
years almost every field in "struct timekeeper" was changed. So this
is almost completely different from his original. Though the key change
in arch/ia64/kernel/fsys.S remains the same.

The core logic change with the updated vsyscall method is that we
preserve the base nanosecond value in shifted nanoseconds, which
allows us to avoid truncating and rounding up to the next nanosecond
every tick to avoid inconsistencies.

Thus the logic moved from
nsec = ((cycle_delta * mult)>>shift) + base_nsec;
to
nsec = ((cycle_delta * mult) + base_snsec) >> shift;

Cc: John Stultz <john.stultz@linaro.org>
Cc: linux-ia64@vger.kernel.org
Signed-off-by: Tony Luck <tony.luck@intel.com>
This commit is contained in:
Tony Luck
2017-10-31 10:43:39 -07:00
parent 0b07194bb5
commit d4d1fc61eb
5 changed files with 35 additions and 25 deletions
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10
arch/ia64/kernel/fsyscall_gtod_data.h
View File

@@ -5,10 +5,16 @@
* fsyscall gettimeofday data
*/
/* like timespec, but includes "shifted nanoseconds" */
struct time_sn_spec {
u64 sec;
u64 snsec;
};
struct fsyscall_gtod_data_t {
seqcount_t seq;
struct timespec wall_time;
struct timespec monotonic_time;
struct time_sn_spec wall_time;
struct time_sn_spec monotonic_time;
u64 clk_mask;
u32 clk_mult;
u32 clk_shift;