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| author | Tony Luck <tony.luck@intel.com> | 2017-10-31 18:43:39 +0100 |
|---|---|---|
| committer | Tony Luck <tony.luck@intel.com> | 2017-10-31 18:58:36 +0100 |
| commit | d4d1fc61eb38ff8e5af657e2d2f2290859a277f2 (patch) | |
| tree | 7ea81dfb26bb9efa59638d7985b8cb49efd6d8bd /arch/ia64/kernel/fsys.S | |
| parent | Linux 4.14-rc7 (diff) | |
| download | linux-d4d1fc61eb38ff8e5af657e2d2f2290859a277f2.tar.xz linux-d4d1fc61eb38ff8e5af657e2d2f2290859a277f2.zip | |
ia64: Update fsyscall gettime to use modern vsyscall_update
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>
Diffstat (limited to 'arch/ia64/kernel/fsys.S')
| -rw-r--r-- | arch/ia64/kernel/fsys.S | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/arch/ia64/kernel/fsys.S b/arch/ia64/kernel/fsys.S index edbf7af95849..0d3c7abb31a8 100644 --- a/arch/ia64/kernel/fsys.S +++ b/arch/ia64/kernel/fsys.S @@ -235,9 +235,9 @@ ENTRY(fsys_gettimeofday) MOV_FROM_ITC(p8, p6, r2, r10) // CPU_TIMER. 36 clocks latency!!! (p9) ld8 r2 = [r30] // MMIO_TIMER. Could also have latency issues.. (p13) ld8 r25 = [r19] // get itc_lastcycle value - ld8 r9 = [r22],IA64_TIMESPEC_TV_NSEC_OFFSET // tv_sec + ld8 r9 = [r22],IA64_TIME_SN_SPEC_SNSEC_OFFSET // sec ;; - ld8 r8 = [r22],-IA64_TIMESPEC_TV_NSEC_OFFSET // tv_nsec + ld8 r8 = [r22],-IA64_TIME_SN_SPEC_SNSEC_OFFSET // snsec (p13) sub r3 = r25,r2 // Diff needed before comparison (thanks davidm) ;; (p13) cmp.gt.unc p6,p7 = r3,r0 // check if it is less than last. p6,p7 cleared @@ -265,9 +265,9 @@ EX(.fail_efault, probe.w.fault r31, 3) mf ;; ld4 r10 = [r20] // gtod_lock.sequence - shr.u r2 = r2,r23 // shift by factor - ;; add r8 = r8,r2 // Add xtime.nsecs + ;; + shr.u r8 = r8,r23 // shift by factor cmp4.ne p7,p0 = r28,r10 (p7) br.cond.dpnt.few .time_redo // sequence number changed, redo // End critical section. |