path: root/arch/ia64
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authorHidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>2007-07-13 16:21:44 -0700
committerTony Luck <tony.luck@intel.com>2007-07-13 16:21:44 -0700
commit829a9996259e4d0b20ce7b94c49b985d6ba6b760 (patch)
tree0ed75d44d279dc233b217a407c7b7f571846235e /arch/ia64
parent83e12a076e3587d60cfbe65a761ef54e14a264e3 (diff)
[IA64] ar.itc access must really be after xtime_lock.sequence has been read
The ".acq" semantics of the load only apply w.r.t. other data access. Reading the clock (ar.itc) isn't a data access so strange things can happen here. Specifically the read of ar.itc can be launched as soon as the read of xtime_lock.sequence is ISSUED. Since this may cache miss, and that might cause a thread switch, and there may be cache contention for the line containing xtime_lock, it may be a long time before the actual value is returned, so the ar.itc value may be very stale. Move the consumption of r28 up before the read of ar.itc to make sure that we really have got the current value of xtime_lock.sequence before look at ar.itc. Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com> Signed-off-by: Tony Luck <tony.luck@intel.com>
Diffstat (limited to 'arch/ia64')
1 files changed, 3 insertions, 1 deletions
diff --git a/arch/ia64/kernel/fsys.S b/arch/ia64/kernel/fsys.S
index 8589e84a27c..3f926c2dc70 100644
--- a/arch/ia64/kernel/fsys.S
+++ b/arch/ia64/kernel/fsys.S
@@ -247,6 +247,9 @@ ENTRY(fsys_gettimeofday)
.pred.rel.mutex p8,p9,p10
ld4.acq r28 = [r29] // xtime_lock.sequence. Must come first for locking purposes
+ ;;
+ and r28 = ~1,r28 // Make sequence even to force retry if odd
+ ;;
(p8) mov r2 = ar.itc // CPU_TIMER. 36 clocks latency!!!
(p9) ld8 r2 = [r30] // readq(ti->address). Could also have latency issues..
@@ -284,7 +287,6 @@ EX(.fail_efault, probe.w.fault r31, 3) // This takes 5 cycles and we have spare
(p15) ld8 r17 = [r19],-IA64_TIMESPEC_TV_NSEC_OFFSET
(p7) cmp.ne p7,p0 = r25,r3 // if cmpxchg not successful redo
// simulate tbit.nz.or p7,p0 = r28,0
- and r28 = ~1,r28 // Make sequence even to force retry if odd
getf.sig r2 = f8
add r8 = r8,r18 // Add time interpolator offset