perf/x86: Fix intel QPI uncore event definitions
John McCalpin reports that the "drs_data" and "ncb_data" QPI
uncore events are missing the "extra bit" and always return zero
values unless the bit is properly set.
More details from him:
According to the Xeon E5-2600 Product Family Uncore Performance
Monitoring Guide, Table 2-94, about 1/2 of the QPI Link Layer events
(including the ones that "perf" calls "drs_data" and "ncb_data") require
that the "extra bit" be set.
This was confusing for a while -- a note at the bottom of page 94 says
that the "extra bit" is bit 16 of the control register.
Unfortunately, Table 2-86 clearly says that bit 16 is reserved and must
be zero. Looking around a bit, I found that bit 21 appears to be the
correct "extra bit", and further investigation shows that "perf" actually
agrees with me:
[root@c560-003.stampede]# cat /sys/bus/event_source/devices/uncore_qpi_0/format/event
config:0-7,21
So the command
# perf -e "uncore_qpi_0/event=drs_data/"
Is the same as
# perf -e "uncore_qpi_0/event=0x02,umask=0x08/"
While it should be
# perf -e "uncore_qpi_0/event=0x102,umask=0x08/"
I confirmed that this last version gives results that agree with the
amount of data that I expected the STREAM benchmark to move across the QPI
link in the second (cross-chip) test of the original script.
Reported-by: John McCalpin <mccalpin@tacc.utexas.edu>
Signed-off-by: Vince Weaver <vincent.weaver@maine.edu>
Cc: zheng.z.yan@intel.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Paul Mackerras <paulus@samba.org>
Cc: <stable@kernel.org>
Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1308021037280.26119@vincent-weaver-1.um.maine.edu
Signed-off-by: Ingo Molnar <mingo@kernel.org>
1 file changed