On 31/01/24 4:56 pm, Kajol Jain wrote:
Running event hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=0/
in one of the system throws below error:
---Logs---
# perf list | grep hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles
hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=?/[Kernel PMU event]
# perf stat -v -e hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=0/ sleep 2
Using CPUID 00800200
Control descriptor is not initialized
Warning:
hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=0/ event is not supported by the kernel.
failed to read counter hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=0/
Performance counter stats for 'system wide':
<not supported> hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=0/
2.000700771 seconds time elapsed
The above error is because of the hcall failure as required
permission "Enable Performance Information Collection" is not set.
Based on current code, single_gpci_request function did not check the
error type incase hcall fails and by default returns EINVAL. But we can
have other reasons for hcall failures like H_AUTHORITY/H_PARAMETER for which
we need to act accordingly.
Fix this issue by adding new checks in the single_gpci_request function.
Result after fix patch changes:
# perf stat -e hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=0/ sleep 2
Error:
No permission to enable hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=0/ event.
Fixes: 220a0c609ad1 ("powerpc/perf: Add support for the hv gpci (get performance counter info) interface")
Reported-by: Akanksha J N <redacted>
Signed-off-by: Kajol Jain <redacted>
Tested the patch on Power10 system, and the fix works fine.
# ./perf stat -v -e hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=1/ sleep 2
Control descriptor is not initialized
hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=1/: 0 2001246376 2001246376
Performance counter stats for 'system wide':
0 hv_gpci/dispatch_timebase_by_processor_processor_time_in_timebase_cycles,phys_processor_idx=1/
2.001250313 seconds time elapsed
Tested-by: Akanksha J N <redacted>
quoted hunk ↗ jump to hunk
---
arch/powerpc/perf/hv-gpci.c | 29 +++++++++++++++++++++++++----
1 file changed, 25 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/perf/hv-gpci.c b/arch/powerpc/perf/hv-gpci.c
index 27f18119fda1..101060facd81 100644
--- a/arch/powerpc/perf/hv-gpci.c
+++ b/arch/powerpc/perf/hv-gpci.c
@@ -695,7 +695,17 @@ static unsigned long single_gpci_request(u32 req, u32 starting_index,
ret = plpar_hcall_norets(H_GET_PERF_COUNTER_INFO,
virt_to_phys(arg), HGPCI_REQ_BUFFER_SIZE);
- if (ret) {
+
+ /*
+ * ret value as 'H_PARAMETER' corresponds to 'GEN_BUF_TOO_SMALL',
+ * which means that the current buffer size cannot accommodate
+ * all the information and a partial buffer returned.
+ * Since in this function we are only accessing data for a given starting index,
+ * we don't need to accommodate whole data and can get required count by
+ * accessing very first entry.
+ * Hence hcall fails only incase the ret value is other than H_SUCCESS or H_PARAMETER.
+ */
+ if (ret && (ret != H_PARAMETER)) {
pr_devel("hcall failed: 0x%lx\n", ret);
goto out;
}@@ -724,7 +734,7 @@ static u64 h_gpci_get_value(struct perf_event *event)
event_get_offset(event),
event_get_length(event),
&count);
- if (ret)
+ if (ret && (ret != H_PARAMETER))
return 0;
return count;
}
@@ -759,6 +769,7 @@ static int h_gpci_event_init(struct perf_event *event)
{
u64 count;
u8 length;
+ unsigned long ret;
/* Not our event */
if (event->attr.type != event->pmu->type)@@ -789,13 +800,23 @@ static int h_gpci_event_init(struct perf_event *event)
}
/* check if the request works... */
- if (single_gpci_request(event_get_request(event),
+ ret = single_gpci_request(event_get_request(event),
event_get_starting_index(event),
event_get_secondary_index(event),
event_get_counter_info_version(event),
event_get_offset(event),
length,
- &count)) {
+ &count);
+
+ /*
+ * ret value as H_AUTHORITY implies that partition is not permitted to retrieve
+ * performance information, and required to set
+ * "Enable Performance Information Collection" option.
+ */
+ if (ret == H_AUTHORITY)
+ return -EPERM;
+
+ if (ret && (ret != H_PARAMETER)) {
pr_devel("gpci hcall failed\n");
return -EINVAL;
}