Re: [PATCH] trace-cruncher: Add API to set tracing CPU affinity

[Yordan Karadzhov <y.karadz@xxxxxxxxx>]

Hi Steven

On 18.12.21 г. 1:26 ч., Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
>
> Add a set_affinity API that can let the user set what CPUs to enable
> tracing on.

For the sake of completeness we will need APIs to 'clear' and 'get' the CPU affinity as well.

> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> ---
> This depends on the new libtracefs API found here:
>
>    https://patchwork.kernel.org/project/linux-trace-devel/patch/20211217180450.12d3524b@xxxxxxxxxxxxxxxxxx/
>
> This can be worked out later if you have comments. And I'll keep
> the VMWare tag, as I did write while still working at VMware. I figured
> that my last patch as a VMware employee would be my first patch
> to trace-cruncher ;-)

This is really symbolic and means a lot for me!

>   examples/test-affinity.py |  5 ++++
>   src/ftracepy-utils.c      | 58 +++++++++++++++++++++++++++++++++++++++
>   src/ftracepy-utils.h      |  3 ++
>   src/ftracepy.c            |  5 ++++
>   4 files changed, 71 insertions(+)
>   create mode 100755 examples/test-affinity.py
>
> diff --git a/examples/test-affinity.py b/examples/test-affinity.py
> new file mode 100755
> index 0000000..1619931
> --- /dev/null
> +++ b/examples/test-affinity.py
> @@ -0,0 +1,5 @@
> +#!/usr/bin/env python3
> +
> +import tracecruncher.ftracepy as ft
> +
> +ft.set_affinity(cpus=["0-1","3"]);
> diff --git a/src/ftracepy-utils.c b/src/ftracepy-utils.c
> index a735d88..ab39cf1 100644
> --- a/src/ftracepy-utils.c
> +++ b/src/ftracepy-utils.c
> @@ -2394,6 +2394,64 @@ PyObject *PyFtrace_hist(PyObject *self, PyObject *args,
>   	return NULL;
>   }
>   
> +PyObject *PyFtrace_set_affinity(PyObject *self, PyObject *args,
> +						PyObject *kwargs)
> +{
> +	struct tracefs_instance *instance;
> +	static char *kwlist[] = {"cpus", "instance", NULL};
> +	PyObject *py_cpus;
> +	PyObject *py_inst = NULL;
> +	const char *cpu_str;
> +	struct trace_seq seq;
> +	int ret;
> +
> +	if (!PyArg_ParseTupleAndKeywords(args,
> +					 kwargs,
> +					 "O|O",
> +					 kwlist,
> +					 &py_cpus,
> +					 &py_inst)) {
> +		return NULL;
> +	}
> +
> +	trace_seq_init(&seq);

There is a global trace_seq object that can be used here. Also you have to check for error.
Perhaps having:

	if (!init_print_seq())
		return NULL;

> +
> +	if (PyUnicode_Check(py_cpus)) {
> +		cpu_str = (const char *)PyUnicode_DATA(py_cpus);
> +		if (trace_seq_puts(&seq, cpu_str) < 0)
> +			goto err_seq;
> +	} else if (PyList_CheckExact(py_cpus)) {
> +		int i, n = PyList_Size(py_cpus);
> +
> +		for (i = 0; i < n; ++i) {
> +			cpu_str = str_from_list(py_cpus, i);
> +			if (i)
> +				trace_seq_putc(&seq, ',');
> +			if (trace_seq_puts(&seq, cpu_str) < 0)
> +				goto err_seq;
> +		}
> +	}
If py_cpus is neither PyUnicode nor PyList, we have to print error and return NULL.

> +
> +	if (!get_optional_instance(py_inst, &instance))
> +		goto err;
> +
> +	trace_seq_terminate(&seq);
> +	ret = tracefs_instance_set_affinity(instance, seq.buffer);
> +	if (ret < 0) {
> +		PyErr_SetString(TRACECRUNCHER_ERROR,
> +				"Invalid \"cpus\" argument.");
> +		goto err;
> +	}
> +
> +	Py_RETURN_NONE;
> +err_seq:
> +	PyErr_SetString(TRACECRUNCHER_ERROR,
> +			"Internal processing string error.");
> +err:
> +	trace_seq_destroy(&seq);
> +	return NULL;
> +}
> +
>   PyObject *PyFtrace_set_ftrace_loglevel(PyObject *self, PyObject *args,
>   						       PyObject *kwargs)
>   {
> diff --git a/src/ftracepy-utils.h b/src/ftracepy-utils.h
> index d09c8bf..67f67ab 100644
> --- a/src/ftracepy-utils.h
> +++ b/src/ftracepy-utils.h
> @@ -208,6 +208,9 @@ PyObject *PyFtrace_register_kretprobe(PyObject *self, PyObject *args,
>   PyObject *PyFtrace_hist(PyObject *self, PyObject *args,
>   					PyObject *kwargs);
>   
> +PyObject *PyFtrace_set_affinity(PyObject *self, PyObject *args,
> +						PyObject *kwargs);
> +
>   PyObject *PyFtrace_set_ftrace_loglevel(PyObject *self, PyObject *args,
>   						       PyObject *kwargs);
>   
> diff --git a/src/ftracepy.c b/src/ftracepy.c
> index b270b71..634f357 100644
> --- a/src/ftracepy.c
> +++ b/src/ftracepy.c
> @@ -377,6 +377,11 @@ static PyMethodDef ftracepy_methods[] = {
>   	 METH_VARARGS | METH_KEYWORDS,
>   	 "Define a histogram."
>   	},
> +	{"set_affinity",
> +	 (PyCFunction) PyFtrace_set_affinity,
> +	 METH_VARARGS | METH_KEYWORDS,
> +	 "Find an existing ftrace instance."
A short description of the method has to be provided here.

Thanks!
Yordan


> +	},
>   	{"set_ftrace_loglevel",
>   	 (PyCFunction) PyFtrace_set_ftrace_loglevel,
>   	 METH_VARARGS | METH_KEYWORDS,