linux-kernel - Re: [PATCH v3 2/2] sched_ext: Add trace point to track sched

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Message-ID: <9db68100-65d0-43e5-a1c0-2aff771f173f@igalia.com>
Date: Tue, 4 Mar 2025 19:39:02 +0900
From: Changwoo Min <changwoo@...lia.com>
To: Andrea Righi <arighi@...dia.com>
Cc: tj@...nel.org, void@...ifault.com, kernel-dev@...lia.com,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] sched_ext: Add trace point to track sched_ext core
 events

Hi Andrea,

On 25. 3. 4. 15:41, Andrea Righi wrote:
> Hi Changwoo,
> 
> On Tue, Mar 04, 2025 at 10:27:40AM +0900, Changwoo Min wrote:
>> Add tracing support to track sched_ext core events
>> (/sched_ext/sched_ext_event). This may be useful for debugging sched_ext
>> schedulers that trigger a particular event.
>>
>> The trace point can be used as other trace points, so it can be used in,
>> for example, `perf trace` and BPF programs, as follows:
>>
>> ======
>> $> sudo perf trace -e sched_ext:sched_ext_event --filter 'name == "SCX_EV_ENQ_SLICE_DFL"'
>> ======
>>
>> ======
>> struct tp_sched_ext_event {
>> 	struct trace_entry ent;
>> 	u32 __data_loc_name;
>> 	s64 delta;
>> };
>>
>> SEC("tracepoint/sched_ext/sched_ext_event")
>> int rtp_add_event(struct tp_sched_ext_event *ctx)
>> {
>> 	char event_name[128];
>> 	unsigned short offset = ctx->__data_loc_name & 0xFFFF;
>>          bpf_probe_read_str((void *)event_name, 128, (char *)ctx + offset);
>>
>> 	bpf_printk("name %s   delta %lld", event_name, ctx->delta);
>> 	return 0;
>> }
>> ======
>>
>> Signed-off-by: Changwoo Min <changwoo@...lia.com>
>> ---
>>   include/trace/events/sched_ext.h | 19 +++++++++++++++++++
>>   kernel/sched/ext.c               |  2 ++
>>   2 files changed, 21 insertions(+)
>>
>> diff --git a/include/trace/events/sched_ext.h b/include/trace/events/sched_ext.h
>> index fe19da7315a9..3d04b9819548 100644
>> --- a/include/trace/events/sched_ext.h
>> +++ b/include/trace/events/sched_ext.h
>> @@ -26,6 +26,25 @@ TRACE_EVENT(sched_ext_dump,
>>   	)
>>   );
>>   
>> +TRACE_EVENT(sched_ext_event,
>> +	    TP_PROTO(const char *name, __u64 delta),
> 
> It shouldn't be __s64 here as well?

Ah, my bad. Thank you for catching this!

> 
> Thanks,
> -Andrea
> 
>> +	    TP_ARGS(name, delta),
>> +
>> +	TP_STRUCT__entry(
>> +		__string(name, name)
>> +		__field(	__s64,		delta		)
>> +	),
>> +
>> +	TP_fast_assign(
>> +		__assign_str(name);
>> +		__entry->delta		= delta;
>> +	),
>> +
>> +	TP_printk("name %s delta %lld",
>> +		  __get_str(name), __entry->delta
>> +	)
>> +);
>> +
>>   #endif /* _TRACE_SCHED_EXT_H */
>>   
>>   /* This part must be outside protection */
>> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
>> index 686629a860f3..debcd1cf2de9 100644
>> --- a/kernel/sched/ext.c
>> +++ b/kernel/sched/ext.c
>> @@ -1554,6 +1554,7 @@ static DEFINE_PER_CPU(struct scx_event_stats, event_stats_cpu);
>>    */
>>   #define scx_add_event(name, cnt) do {						\
>>   	this_cpu_add(event_stats_cpu.name, cnt);				\
>> +	trace_sched_ext_event(#name, cnt);					\
>>   } while(0)
>>   
>>   /**
>> @@ -1565,6 +1566,7 @@ static DEFINE_PER_CPU(struct scx_event_stats, event_stats_cpu);
>>    */
>>   #define __scx_add_event(name, cnt) do {						\
>>   	__this_cpu_add(event_stats_cpu.name, cnt);				\
>> +	trace_sched_ext_event(#name, cnt);					\
>>   } while(0)
>>   
>>   /**
>> -- 
>> 2.48.1
>>
>