Re: [PATCH v10 02/11] arm64: Make perf_callchain_kernel() use arch_stack_walk()

Mark Rutland
2021-10-22T18:12:04Z

On Thu, Oct 14, 2021 at 09:58:38PM -0500, madvenka@linux.microsoft.com wrote:
> From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>
>
> Currently, perf_callchain_kernel() in ARM64 code walks the stack using
> start_backtrace() and walk_stackframe(). Make it use arch_stack_walk()
> instead. This makes maintenance easier.
>
> Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>

This looks good to me; bailing out when perf_callchain_store() can't
accept any more entries absolutely makes sense.

I gave this a spin with:

| # perf record -g -c1 ls
| # perf report

... and the recorded callchains look sane.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>

As mentioned on patch 1, I'd like to get this rebased atop Peter's
untangling of ARCH_STACKWALK from STACKTRACE.

Thanks,
Mark.

> ---
> arch/arm64/kernel/perf_callchain.c | 8 ++------
> 1 file changed, 2 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm64/kernel/perf_callchain.c b/arch/arm64/kernel/perf_callchain.c
> index 4a72c2727309..f173c448e852 100644
> --- a/arch/arm64/kernel/perf_callchain.c
> +++ b/arch/arm64/kernel/perf_callchain.c
> @@ -140,22 +140,18 @@ void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
> static bool callchain_trace(void *data, unsigned long pc)
> {
> struct perf_callchain_entry_ctx *entry = data;
> - perf_callchain_store(entry, pc);
> - return true;
> + return perf_callchain_store(entry, pc) == 0;
> }
>
> void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
> struct pt_regs *regs)
> {
> - struct stackframe frame;
> -
> if (perf_guest_cbs && perf_guest_cbs->is_in_guest()) {
> /* We don't support guest os callchain now */
> return;
> }
>
> - start_backtrace(&frame, regs->regs[29], regs->pc);
> - walk_stackframe(current, &frame, callchain_trace, entry);
> + arch_stack_walk(callchain_trace, entry, current, regs);
> }
>
> unsigned long perf_instruction_pointer(struct pt_regs *regs)
> --
> 2.25.1
>