[PATCH] perf vendor events: Fix DRAM_BW_Use 0 issue for CLX/SKX

[Jin Yao]

Ian reports an issue that the metric DRAM_BW_Use often remains 0.

The metric expression for DRAM_BW_Use on CLX/SKX:

"( 64 * ( uncore_imc@cas_count_read@ + uncore_imc@cas_count_write@ ) / 1000000000 ) / duration_time"

The counts of uncore_imc/cas_count_read/ and uncore_imc/cas_count_write/
are scaled up by 64, that is to turn a count of cache lines into bytes,
the count is then divided by 1000000000 to give GB.

However, the counts of uncore_imc/cas_count_read/ and
uncore_imc/cas_count_write/ have been scaled yet.

The scale values are from sysfs, such as
/sys/devices/uncore_imc_0/events/cas_count_read.scale.
It's 6.103515625e-5 (64 / 1024.0 / 1024.0).

So if we use original metric expression, the result is not correct.

But the difficulty is, for SKL client, the counts are not scaled.

The metric expression for DRAM_BW_Use on SKL:

"64 * ( arb@event\\=0x81\\,umask\\=0x1@ + arb@event\\=0x84\\,umask\\=0x1@ ) / 1000000 / duration_time / 1000"

root@kbl-ppc:~# perf stat -M DRAM_BW_Use -a -- sleep 1

 Performance counter stats for 'system wide':

               190      arb/event=0x84,umask=0x1/ #     1.86 DRAM_BW_Use
        29,093,178      arb/event=0x81,umask=0x1/
     1,000,703,287 ns   duration_time

       1.000703287 seconds time elapsed

The result is expected.

So the easy way is just change the metric expression for CLX/SKX.
This patch changes the metric expression to:

"( ( ( uncore_imc@cas_count_read@ + uncore_imc@cas_count_write@ ) * 1048576 ) / 1000000000 ) / duration_time"

1048576 = 1024 * 1024.

Before (tested on CLX):

root@lkp-csl-2sp5 ~# perf stat -M DRAM_BW_Use -a -- sleep 1

 Performance counter stats for 'system wide':

            765.35 MiB  uncore_imc/cas_count_read/ #     0.00 DRAM_BW_Use
              5.42 MiB  uncore_imc/cas_count_write/
        1001515088 ns   duration_time

       1.001515088 seconds time elapsed

After:

root@lkp-csl-2sp5 ~# perf stat -M DRAM_BW_Use -a -- sleep 1

 Performance counter stats for 'system wide':

            767.95 MiB  uncore_imc/cas_count_read/ #     0.80 DRAM_BW_Use
              5.02 MiB  uncore_imc/cas_count_write/
        1001900010 ns   duration_time

       1.001900010 seconds time elapsed

Fixes: 038d3b53c284 ("perf vendor events intel: Update CascadelakeX events to v1.08")
Fixes: b5ff7f2799a4 ("perf vendor events: Update SkylakeX events to v1.21")
Signed-off-by: Jin Yao <yao.jin@xxxxxxxxxxxxxxx>
---
 tools/perf/pmu-events/arch/x86/cascadelakex/clx-metrics.json | 2 +-
 tools/perf/pmu-events/arch/x86/skylakex/skx-metrics.json     | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/perf/pmu-events/arch/x86/cascadelakex/clx-metrics.json b/tools/perf/pmu-events/arch/x86/cascadelakex/clx-metrics.json
index de3193552277..00f4fcffa815 100644
--- a/tools/perf/pmu-events/arch/x86/cascadelakex/clx-metrics.json
+++ b/tools/perf/pmu-events/arch/x86/cascadelakex/clx-metrics.json
@@ -329,7 +329,7 @@
     },
     {
         "BriefDescription": "Average external Memory Bandwidth Use for reads and writes [GB / sec]",
-        "MetricExpr": "( 64 * ( uncore_imc@cas_count_read@ + uncore_imc@cas_count_write@ ) / 1000000000 ) / duration_time",
+        "MetricExpr": "( ( ( uncore_imc@cas_count_read@ + uncore_imc@cas_count_write@ ) * 1048576 ) / 1000000000 ) / duration_time",
         "MetricGroup": "Memory_BW;SoC",
         "MetricName": "DRAM_BW_Use"
     },
diff --git a/tools/perf/pmu-events/arch/x86/skylakex/skx-metrics.json b/tools/perf/pmu-events/arch/x86/skylakex/skx-metrics.json
index f31794d3b926..0dd8b13b5cfb 100644
--- a/tools/perf/pmu-events/arch/x86/skylakex/skx-metrics.json
+++ b/tools/perf/pmu-events/arch/x86/skylakex/skx-metrics.json
@@ -323,7 +323,7 @@
     },
     {
         "BriefDescription": "Average external Memory Bandwidth Use for reads and writes [GB / sec]",
-        "MetricExpr": "( 64 * ( uncore_imc@cas_count_read@ + uncore_imc@cas_count_write@ ) / 1000000000 ) / duration_time",
+        "MetricExpr": "( ( ( uncore_imc@cas_count_read@ + uncore_imc@cas_count_write@ ) * 1048576 ) / 1000000000 ) / duration_time",
         "MetricGroup": "Memory_BW;SoC",
         "MetricName": "DRAM_BW_Use"
     },
-- 
2.17.1