linux-kernel - Re: [PATCH v2 3/3] ftrace: Add sample with custom ops

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Message-ID: <20230206222516.GA873421@roeck-us.net>
Date:   Mon, 6 Feb 2023 14:25:16 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-kernel@...r.kernel.org, mhiramat@...nel.org,
        revest@...omium.org, rostedt@...dmis.org,
        linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] ftrace: Add sample with custom ops

On Tue, Jan 03, 2023 at 12:49:12PM +0000, Mark Rutland wrote:
> When reworking core ftrace code or architectural ftrace code, it's often
> necessary to test/analyse/benchmark a number of ftrace_ops
> configurations. This patch adds a module which can be used to explore
> some of those configurations.
> 
> I'm using this to benchmark various options for changing the way
> trampolines and handling of ftrace_ops work on arm64, and ensuring other
> architectures aren't adversely affected.
> 
> For example, in a QEMU+KVM VM running on a 2GHz Xeon E5-2660
> workstation, loading the module in various configurations produces:
> 
...

> +++ b/samples/ftrace/ftrace-ops.c

...

> +static int __init ftrace_ops_sample_init(void)
> +{
> +	unsigned long flags = 0;
> +	ktime_t start, end;
> +	u64 period;
> +
...
> +
> +	period = ktime_to_ns(ktime_sub(end, start));
> +
> +	pr_info("Attempted %u calls to %ps in %lluns (%lluns / call)\n",
> +		nr_function_calls, tracee_relevant,
> +		period, period / nr_function_calls);
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^

Building csky:allmodconfig ... failed
--------------
Error log:
ERROR: modpost: "__udivdi3" [samples/ftrace/ftrace-ops.ko] undefined!

Guenter