* [PATCH] ftrace: sample: avoid open-coded 64-bit division
@ 2023-01-30 13:02 Arnd Bergmann
2023-01-30 13:07 ` Mark Rutland
0 siblings, 1 reply; 2+ messages in thread
From: Arnd Bergmann @ 2023-01-30 13:02 UTC (permalink / raw)
To: Steven Rostedt, Masami Hiramatsu, Mark Rutland
Cc: Arnd Bergmann, linux-kernel, linux-trace-kernel
From: Arnd Bergmann <arnd@arndb.de>
Calculating the average period requires a 64-bit division that leads
to a link failure on 32-bit architectures:
x86_64-linux-ld: samples/ftrace/ftrace-ops.o: in function `ftrace_ops_sample_init':
ftrace-ops.c:(.init.text+0x23b): undefined reference to `__udivdi3'
Use the div_u64() helper to do this instead. Since this is an init function that
is not called frequently, the runtime overhead is going to be acceptable.
Fixes: b56c68f705ca ("ftrace: Add sample with custom ops")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
samples/ftrace/ftrace-ops.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/samples/ftrace/ftrace-ops.c b/samples/ftrace/ftrace-ops.c
index 24deb51c7261..0c8da87ff5c3 100644
--- a/samples/ftrace/ftrace-ops.c
+++ b/samples/ftrace/ftrace-ops.c
@@ -223,7 +223,7 @@ static int __init ftrace_ops_sample_init(void)
pr_info("Attempted %u calls to %ps in %lluns (%lluns / call)\n",
nr_function_calls, tracee_relevant,
- period, period / nr_function_calls);
+ period, div_u64(period, nr_function_calls));
if (persist)
return 0;
--
2.39.0
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] ftrace: sample: avoid open-coded 64-bit division
2023-01-30 13:02 [PATCH] ftrace: sample: avoid open-coded 64-bit division Arnd Bergmann
@ 2023-01-30 13:07 ` Mark Rutland
0 siblings, 0 replies; 2+ messages in thread
From: Mark Rutland @ 2023-01-30 13:07 UTC (permalink / raw)
To: Arnd Bergmann
Cc: Steven Rostedt, Masami Hiramatsu, Arnd Bergmann, linux-kernel,
linux-trace-kernel
On Mon, Jan 30, 2023 at 02:02:37PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>
> Calculating the average period requires a 64-bit division that leads
> to a link failure on 32-bit architectures:
>
> x86_64-linux-ld: samples/ftrace/ftrace-ops.o: in function `ftrace_ops_sample_init':
> ftrace-ops.c:(.init.text+0x23b): undefined reference to `__udivdi3'
Whoops; sorry about that.
> Use the div_u64() helper to do this instead. Since this is an init function that
> is not called frequently, the runtime overhead is going to be acceptable.
>
> Fixes: b56c68f705ca ("ftrace: Add sample with custom ops")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Mark.
> ---
> samples/ftrace/ftrace-ops.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/samples/ftrace/ftrace-ops.c b/samples/ftrace/ftrace-ops.c
> index 24deb51c7261..0c8da87ff5c3 100644
> --- a/samples/ftrace/ftrace-ops.c
> +++ b/samples/ftrace/ftrace-ops.c
> @@ -223,7 +223,7 @@ static int __init ftrace_ops_sample_init(void)
>
> pr_info("Attempted %u calls to %ps in %lluns (%lluns / call)\n",
> nr_function_calls, tracee_relevant,
> - period, period / nr_function_calls);
> + period, div_u64(period, nr_function_calls));
>
> if (persist)
> return 0;
> --
> 2.39.0
>
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