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Message-ID: <xhsmhv8gzi8uw.mognet@vschneid.remote.csb>
Date: Thu, 11 May 2023 09:13:27 +0100
From: Valentin Schneider <vschneid@...hat.com>
To: Leonardo Brás <leobras@...hat.com>,
Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Yury Norov <yury.norov@...il.com>,
"Paul E. McKenney" <paulmck@...nel.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Nadav Amit <namit@...are.com>,
Zhen Lei <thunder.leizhen@...wei.com>,
Chen Zhongjin <chenzhongjin@...wei.com>,
linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
Marcelo Tosatti <mtosatti@...hat.com>,
Daniel Bristot de Oliveira <bristot@...nel.org>
Subject: Re: [RFC PATCH 1/1] smp: Add tracepoints for functions called with
smp_call_function*()
On 10/05/23 17:27, Leonardo Brás wrote:
> On Thu, 2023-05-04 at 12:59 +0100, Valentin Schneider wrote:
>> +TRACE_EVENT(csd_queue_cpu,
>> +
>> + TP_PROTO(const unsigned int cpu,
>> + unsigned long callsite,
>> + smp_call_func_t func,
>> + call_single_data_t *csd),
>> +
>> + TP_ARGS(cpu, callsite, func, csd),
>> +
>> + TP_STRUCT__entry(
>> + __field(unsigned int, cpu)
>> + __field(void *, callsite)
>> + __field(void *, func)
>> + __field(void *, csd)
>> + ),
>> +
>> + TP_fast_assign(
>> + __entry->cpu = cpu;
>> + __entry->callsite = (void *)callsite;
>> + __entry->func = func;
>> + __entry->csd = csd;
>> + ),
>> +
>> + TP_printk("cpu=%u callsite=%pS func=%pS csd=%p",
>> + __entry->cpu, __entry->callsite, __entry->func, __entry->csd)
>> +);
>
> This is for the caller side, right?
>
Yep, see usage lower down.
>> +
>> +DECLARE_EVENT_CLASS(csd_function,
>> +
>> + TP_PROTO(smp_call_func_t func, call_single_data_t *csd),
>> +
>> + TP_ARGS(func, csd),
>> +
>> + TP_STRUCT__entry(
>> + __field(void *, func)
>> + __field(void *, csd)
>> + ),
>> +
>> + TP_fast_assign(
>> + __entry->func = func;
>> + __entry->csd = csd;
>> + ),
>> +
>> + TP_printk("func=%pS csd=%p", __entry->func, __entry->csd)
>> +);
>> +
>> +DEFINE_EVENT(csd_function, csd_function_entry,
>> + TP_PROTO(smp_call_func_t func, call_single_data_t *csd),
>> + TP_ARGS(func, csd)
>> +);
>> +
>> +DEFINE_EVENT(csd_function, csd_function_exit,
>> + TP_PROTO(smp_call_func_t func, call_single_data_t *csd),
>> + TP_ARGS(func, csd)
>> +);
>
> Oh, this is what event_class is for. Thanks for the example :)
>
>> +
>> +#endif /* _TRACE_SMP_H */
>> +
>> +/* This part must be outside protection */
>> +#include <trace/define_trace.h>
>> diff --git a/kernel/smp.c b/kernel/smp.c
>> index ab3e5dad6cfe9..7d28db303e9bc 100644
>> --- a/kernel/smp.c
>> +++ b/kernel/smp.c
>> @@ -27,6 +27,9 @@
>> #include <linux/jump_label.h>
>>
>> #include <trace/events/ipi.h>
>> +#define CREATE_TRACE_POINTS
>> +#include <trace/events/smp.h>
>> +#undef CREATE_TRACE_POINTS
>>
>> #include "smpboot.h"
>> #include "sched/smp.h"
>> @@ -121,6 +124,14 @@ send_call_function_ipi_mask(struct cpumask *mask)
>> arch_send_call_function_ipi_mask(mask);
>> }
>>
>> +static __always_inline void
>> +csd_do_func(smp_call_func_t func, void *info, call_single_data_t *csd)
>> +{
>> + trace_csd_function_entry(func, csd);
>> + func(info);
>> + trace_csd_function_exit(func, csd);
>> +}
>> +
>
> Good one, a helper to avoid calling those traces everywhere.
>
> Honest question:
> Since info == csd->info and func == csd->func, we could just pass csd, right?
> I suppose the suggestion on the 3-argument version is to use the values already
> fetched from memory instead of fetching them again. Is that correct?
>
There's also the special case of CSD_TYPE_TTWU where there is no csd->func,
instead we have an implicit func mapping to sched_ttwu_pending). I think
it's preferable to directly feed the right things to the TP than to
duplicate the "decoding" logic against the *csd passed as TP argument.
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