[PATCH] trace-cmd: Fix trace_tsc2nsec_is_supported() on !x86

[PATCH] trace-cmd: Fix trace_tsc2nsec_is_supported() on !x86

[Nicolas Saenz Julienne]

'trace-cmd list -C' outputs 'tsc2nsec' on my arm64 machine. TSC is an
x86 specific counter, so it shouldn't be supported. Fix this by making
sure TSC exists as a trace clock in trace_tsc2nsec_is_supported().

Signed-off-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
---
 tracecmd/trace-record.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
index 1767a6c..78e9566 100644
--- a/tracecmd/trace-record.c
+++ b/tracecmd/trace-record.c
@@ -6122,6 +6122,9 @@ static int get_tsc_nsec(int *shift, int *mult)
 
 bool trace_tsc2nsec_is_supported(void)
 {
+	if (!clock_is_supported(NULL, TSC_CLOCK))
+		return false;
+
 	return get_tsc_nsec(NULL, NULL) == 0;
 }
 
-- 
2.33.1

Re: [PATCH] trace-cmd: Fix trace_tsc2nsec_is_supported() on !x86

[Steven Rostedt]

On Tue, 16 Nov 2021 20:21:52 +0100
Nicolas Saenz Julienne <nsaenzju@redhat.com> wrote:

> 'trace-cmd list -C' outputs 'tsc2nsec' on my arm64 machine. TSC is an
> x86 specific counter, so it shouldn't be supported. Fix this by making
> sure TSC exists as a trace clock in trace_tsc2nsec_is_supported().

TSC is just an acronym for Time Stamp Counter. Yes, x86 calls it the TSC,
but really it can be any raw clock.

If arm or any other arch has a raw clock that can write directly to the
ring buffer, and perf has a way to convert that to nsecs, we should still
be able to support it. For instance, I believe that powerpc has a ppc-tb
clock that is similar to the tsc of x86. We probably should allow that too.

Hmm, I wonder if the kernel should have a "raw_clock" if the raw time stamp
is used for any arch, and the tsc2nsec can still be used if raw_clock is
supported.

That said, I agree that we should verify that the raw clock that is
converted is available along with the perf info.

-- Steve


> 
> Signed-off-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
> ---
>  tracecmd/trace-record.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
> index 1767a6c..78e9566 100644
> --- a/tracecmd/trace-record.c
> +++ b/tracecmd/trace-record.c
> @@ -6122,6 +6122,9 @@ static int get_tsc_nsec(int *shift, int *mult)
>  
>  bool trace_tsc2nsec_is_supported(void)
>  {
> +	if (!clock_is_supported(NULL, TSC_CLOCK))
> +		return false;
> +
>  	return get_tsc_nsec(NULL, NULL) == 0;
>  }
>