Author: zml
Date: Mon Jun 4 16:04:01 2012
New Revision: 236566
URL: http://svn.freebsd.org/changeset/base/236566
Log:
Fix DTrace TSC skew calculation:
The skew calculation here is exactly backwards. We were able to repro
it on a multi-package ESX server running a FreeBSD VM, where the TSCs
can be pretty evil.
MFC after: 1 week
Submitted by: Jeff Ford <jeffrey.fo...@isilon.com>
Reviewed by: avg, gnn
Modified:
head/sys/cddl/dev/dtrace/amd64/dtrace_subr.c
head/sys/cddl/dev/dtrace/i386/dtrace_subr.c
Modified: head/sys/cddl/dev/dtrace/amd64/dtrace_subr.c
==============================================================================
--- head/sys/cddl/dev/dtrace/amd64/dtrace_subr.c Mon Jun 4 15:21:13
2012 (r236565)
+++ head/sys/cddl/dev/dtrace/amd64/dtrace_subr.c Mon Jun 4 16:04:01
2012 (r236566)
@@ -446,7 +446,7 @@ dtrace_gethrtime()
* (see nsec_scale calculations) taking into account 32-bit shift of
* the higher half and finally add.
*/
- tsc = rdtsc() + tsc_skew[curcpu];
+ tsc = rdtsc() - tsc_skew[curcpu];
lo = tsc;
hi = tsc >> 32;
return (((lo * nsec_scale) >> SCALE_SHIFT) +
Modified: head/sys/cddl/dev/dtrace/i386/dtrace_subr.c
==============================================================================
--- head/sys/cddl/dev/dtrace/i386/dtrace_subr.c Mon Jun 4 15:21:13 2012
(r236565)
+++ head/sys/cddl/dev/dtrace/i386/dtrace_subr.c Mon Jun 4 16:04:01 2012
(r236566)
@@ -447,7 +447,7 @@ dtrace_gethrtime()
* (see nsec_scale calculations) taking into account 32-bit shift of
* the higher half and finally add.
*/
- tsc = rdtsc() + tsc_skew[curcpu];
+ tsc = rdtsc() - tsc_skew[curcpu];
lo = tsc;
hi = tsc >> 32;
return (((lo * nsec_scale) >> SCALE_SHIFT) +
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