On 2024/3/8 1:52, Conor Dooley wrote:
On Tue, Mar 05, 2024 at 03:52:23PM +0000, Pu Lehui wrote:
From: Pu Lehui <pulehui@xxxxxxxxxx>
RISC-V perf does not yet support branch sampling. Two riscv bpf
testcases get_branch_snapshot and perf_branches/perf_branches_hw failed
due to not disabling such sampling.
Signed-off-by: Pu Lehui <pulehui@xxxxxxxxxx>
This seems worthy of a fixes tag. For what commit I do not know, but I
figure it is a problem currently in mainline and a fix should be
backported?
Thanks for review. We need to ban this type of event, otherwise we will
get unpredictable results. It should be with a fixes tag.
---
drivers/perf/riscv_pmu.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/drivers/perf/riscv_pmu.c b/drivers/perf/riscv_pmu.c
index c78a6fd6c57f..bc42cb95a97c 100644
--- a/drivers/perf/riscv_pmu.c
+++ b/drivers/perf/riscv_pmu.c
@@ -313,6 +313,10 @@ static int riscv_pmu_event_init(struct perf_event *event)
u64 event_config = 0;
uint64_t cmask;
+ /* does not support taken branch sampling */
Skimming patchwork, I found this comment confusing.
Isolated from the commit message, which it will be once committed, it
was not immediately clear that you were referring to the driver. I think
it is just matter of making this a complete sentence that starts by
mentioning /what/ does not support this feature. Is it the driver? Does
the spec not allow it? etc
I actually just found out that the current implementation of riscv perf
driver doesn't support it. After reading the relevant spec, I did not
find any description related to branch record. Maybe I may have missed
something or it may be supported in the future, but the current driver
does not support it, so I think it is more appropriate to limit this
comment to the driver implementation. How about "riscv perf driver does
not support branch stack sampling"?
Cheers,
Conor.
+ if (has_branch_stack(event))
+ return -EOPNOTSUPP;
+
hwc->flags = 0;
mapped_event = rvpmu->event_map(event, &event_config);
if (mapped_event < 0) {
--
2.34.1
