Re: [PATCH V2] ARM: trace: Add tracepoint for the Inter ProcessorInterrupt

From: Daniel Lezcano
Date: Fri Oct 25 2013 - 18:26:05 EST

On 10/25/2013 10:09 AM, Steven Rostedt wrote:
On Fri, 2013-10-25 at 08:49 +0200, Daniel Lezcano wrote:
On 10/15/2013 02:10 PM, Daniel Lezcano wrote:
The Inter Processor Interrupt is used on ARM to tell another processor to do
a specific action. This is mainly used to emulate a timer interrupt on an idle
cpu, force a cpu to reschedule or run a function on another processor context.

Add a tracepoint when raising an IPI and in the entry/exit handler functions.

When a cpu raises an IPI, the targeted cpus is an interesting information, the
cpumask conversion in hexa is added in the trace using the cpumask_scnprintf

Tested-on Vexpress TC2 (5 processors).

Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>

Hi All,

does this patch sound good for inclusion ?

Ug, I never sent my email. It was half written and in my drafts folder.

That's just typical ! I think no one can say it never happened :)

I'll reply below.

[ ... ]

+ * ipi_raise - called when a smp cross call is made
+ * @ipinr: the IPI number
+ * @cpumask: the recipients for the IPI
+ *
+ * The @ipinr value must be valid and the action name associated with
+ * the IPI value is given in the trace as well as the cpumask of the
+ * targeted cpus.
+ */
+ TP_PROTO(const struct cpumask *cpumask, int ipinr),
+ TP_ARGS(cpumask, ipinr),
+ TP_CONDITION(ipinr < NR_IPI && ipinr >= 0),
+ TP_STRUCT__entry(
+ __field(int, ipinr)
+ __array(char, cpumask, NR_CPUS)
+ ),
+ TP_fast_assign(
+ __entry->ipinr = ipinr;
+ cpumask_scnprintf(__entry->cpumask,
+ ARRAY_SIZE(__entry->cpumask), cpumask);

Please do not do the scnprintf() in the TP_fast_assign(). It's heavy
weight and this is done in the code path. Just copy the actual cpumask


Now, how to do that exactly is the reason I never sent my original mail,
because I never got around to looking how to do it, but it is possible.
Unfortunately, I'm at Kernel Summit at the moment, and still don't have
time to look at the best way to do it. But you can use dynamic arrays
for the cpus_online.

+ ),
+ TP_printk("ipi=%d, cpumask=0x%s, name=%s", __entry->ipinr, __entry->cpumask,
+ show_ipi_name(__entry->ipinr))

Here is where you can convert the cpumask saved in the ring buffer to a
snprintf() format. Now this may need some work too, and perhaps even a
handler to help. I thought there was already some printk format that
does cpumasks.

If the helpers are not there, then I can work on adding some.

I don't find any helper in the code except cpumask_scnprintf. If you don't have the time, I can do the adequate changes with some advices.

-- Daniel

+#endif /* _TRACE_IPI_H */
+/* This part must be outside protection */
+#include <trace/define_trace.h>

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