[v2] drivers/perf: riscv: Disable PERF_SAMPLE_BRANCH_* while not supported

Commit Message

Pu Lehui March 12, 2024, 1:20 a.m. UTC

From: Pu Lehui <[e-mail]>

RISC-V perf driver does not yet support branch sampling. Although the
specification is in the works [0], it is best to disable such events
until support is available, otherwise we will get unexpected results.
Due to this reason, two riscv bpf testcases get_branch_snapshot and
perf_branches/perf_branches_hw fail.

Link: https://github.com/riscv/riscv-control-transfer-records [0]
Fixes: f5bfa23f576f ("RISC-V: Add a perf core library for pmu drivers")
Signed-off-by: Pu Lehui <[e-mail]>
---
 drivers/perf/riscv_pmu.c | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Conor Dooley March 12, 2024, 12:52 p.m. UTC | #1

On Tue, Mar 12, 2024 at 01:20:53AM +0000, Pu Lehui wrote:
> From: Pu Lehui <[e-mail]>
> 
> RISC-V perf driver does not yet support branch sampling. Although the
> specification is in the works [0], it is best to disable such events
> until support is available, otherwise we will get unexpected results.
> Due to this reason, two riscv bpf testcases get_branch_snapshot and
> perf_branches/perf_branches_hw fail.
> 
> Link: https://github.com/riscv/riscv-control-transfer-records [0]
> Fixes: f5bfa23f576f ("RISC-V: Add a perf core library for pmu drivers")
> Signed-off-by: Pu Lehui <[e-mail]>

Reviewed-by: Conor Dooley <[e-mail]>

Thanks,
Conor.

Atish Patra March 12, 2024, 7:12 p.m. UTC | #2

On Mon, Mar 11, 2024 at 6:19 PM Pu Lehui <[e-mail]> wrote:
>
> From: Pu Lehui <[e-mail]>
>
> RISC-V perf driver does not yet support branch sampling. Although the
> specification is in the works [0], it is best to disable such events
> until support is available, otherwise we will get unexpected results.
> Due to this reason, two riscv bpf testcases get_branch_snapshot and
> perf_branches/perf_branches_hw fail.
>
> Link: https://github.com/riscv/riscv-control-transfer-records [0]
> Fixes: f5bfa23f576f ("RISC-V: Add a perf core library for pmu drivers")
> Signed-off-by: Pu Lehui <[e-mail]>
> ---
>  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..b4efdddb2ad9 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;
>
> +       /* driver does not support branch stack sampling */
> +       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
>


Reviewed-by: Atish Patra <[e-mail]>

[e-mail] March 27, 2024, 2 p.m. UTC | #3

Hello:

This patch was applied to riscv/linux.git (fixes)
by Palmer Dabbelt <[e-mail]>:

On Tue, 12 Mar 2024 01:20:53 +0000 you wrote:
> From: Pu Lehui <[e-mail]>
> 
> RISC-V perf driver does not yet support branch sampling. Although the
> specification is in the works [0], it is best to disable such events
> until support is available, otherwise we will get unexpected results.
> Due to this reason, two riscv bpf testcases get_branch_snapshot and
> perf_branches/perf_branches_hw fail.
> 
> [...]

Here is the summary with links:
  - [v2] drivers/perf: riscv: Disable PERF_SAMPLE_BRANCH_* while not supported
    https://git.kernel.org/riscv/c/ea6873118493

You are awesome, thank you!

Patch

diff --git a/drivers/perf/riscv_pmu.c b/drivers/perf/riscv_pmu.c
index c78a6fd6c57f..b4efdddb2ad9 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;
 
+	/* driver does not support branch stack sampling */
+	if (has_branch_stack(event))
+		return -EOPNOTSUPP;
+
 	hwc->flags = 0;
 	mapped_event = rvpmu->event_map(event, &event_config);
 	if (mapped_event < 0) {