linux-kernel - Re: [RFC PATCH 46/86] tracing: handle lazy resched

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Date:   Wed, 08 Nov 2023 01:24:10 -0800
From:   Ankur Arora <ankur.a.arora@...cle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Ankur Arora <ankur.a.arora@...cle.com>,
        linux-kernel@...r.kernel.org, tglx@...utronix.de,
        peterz@...radead.org, torvalds@...ux-foundation.org,
        paulmck@...nel.org, linux-mm@...ck.org, x86@...nel.org,
        akpm@...ux-foundation.org, luto@...nel.org, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        willy@...radead.org, mgorman@...e.de, jon.grimm@....com,
        bharata@....com, raghavendra.kt@....com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        jgross@...e.com, andrew.cooper3@...rix.com, mingo@...nel.org,
        bristot@...nel.org, mathieu.desnoyers@...icios.com,
        glaubitz@...sik.fu-berlin.de, anton.ivanov@...bridgegreys.com,
        krypton@...ich-teichert.org, David.Laight@...LAB.COM,
        richard@....at, mjguzik@...il.com,
        Richard Henderson <richard.henderson@...aro.org>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>, linux-alpha@...r.kernel.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k@...ts.linux-m68k.org, Dinh Nguyen <dinguyen@...nel.org>
Subject: Re: [RFC PATCH 46/86] tracing: handle lazy resched


Steven Rostedt <rostedt@...dmis.org> writes:

> On Tue,  7 Nov 2023 13:57:32 -0800
> Ankur Arora <ankur.a.arora@...cle.com> wrote:
>
>> Tracing support.
>>
>> Note: this is quite incomplete.
>
> What's not complete? The removal of the IRQS_NOSUPPORT?
>
> Really, that's only for alpha, m68k and nios2. I think setting 'X' is not
> needed anymore, and we can use that bit for this, and for those archs, have
> 0 for interrupts disabled.

Right, that makes sense. I wasn't worried about the IRQS_NOSUPPORT.
I think I just misread the code and thought that some other tracers might
need separate support as well.

Will fix the commit message.

Thanks
Ankur

>>
>> Originally-by: Thomas Gleixner <tglx@...utronix.de>
>> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
>> ---
>>  include/linux/trace_events.h |  6 +++---
>>  kernel/trace/trace.c         |  2 ++
>>  kernel/trace/trace_output.c  | 16 ++++++++++++++--
>>  3 files changed, 19 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
>> index 21ae37e49319..355d25d5e398 100644
>> --- a/include/linux/trace_events.h
>> +++ b/include/linux/trace_events.h
>> @@ -178,7 +178,7 @@ unsigned int tracing_gen_ctx_irq_test(unsigned int irqs_status);
>>
>>  enum trace_flag_type {
>>  	TRACE_FLAG_IRQS_OFF		= 0x01,
>> -	TRACE_FLAG_IRQS_NOSUPPORT	= 0x02,
>> +	TRACE_FLAG_NEED_RESCHED_LAZY    = 0x02,
>>  	TRACE_FLAG_NEED_RESCHED		= 0x04,
>>  	TRACE_FLAG_HARDIRQ		= 0x08,
>>  	TRACE_FLAG_SOFTIRQ		= 0x10,
>> @@ -205,11 +205,11 @@ static inline unsigned int tracing_gen_ctx(void)
>>
>>  static inline unsigned int tracing_gen_ctx_flags(unsigned long irqflags)
>>  {
>> -	return tracing_gen_ctx_irq_test(TRACE_FLAG_IRQS_NOSUPPORT);
>> +	return tracing_gen_ctx_irq_test(0);
>>  }
>>  static inline unsigned int tracing_gen_ctx(void)
>>  {
>> -	return tracing_gen_ctx_irq_test(TRACE_FLAG_IRQS_NOSUPPORT);
>> +	return tracing_gen_ctx_irq_test(0);
>>  }
>>  #endif
>>
>> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
>> index 7f067ad9cf50..0776dba32c2d 100644
>> --- a/kernel/trace/trace.c
>> +++ b/kernel/trace/trace.c
>> @@ -2722,6 +2722,8 @@ unsigned int tracing_gen_ctx_irq_test(unsigned int irqs_status)
>>
>>  	if (tif_need_resched(RESCHED_eager))
>>  		trace_flags |= TRACE_FLAG_NEED_RESCHED;
>> +	if (tif_need_resched(RESCHED_lazy))
>> +		trace_flags |= TRACE_FLAG_NEED_RESCHED_LAZY;
>>  	if (test_preempt_need_resched())
>>  		trace_flags |= TRACE_FLAG_PREEMPT_RESCHED;
>>  	return (trace_flags << 16) | (min_t(unsigned int, pc & 0xff, 0xf)) |
>> diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
>> index db575094c498..c251a44ad8ac 100644
>> --- a/kernel/trace/trace_output.c
>> +++ b/kernel/trace/trace_output.c
>> @@ -460,17 +460,29 @@ int trace_print_lat_fmt(struct trace_seq *s, struct trace_entry *entry)
>>  		(entry->flags & TRACE_FLAG_IRQS_OFF && bh_off) ? 'D' :
>>  		(entry->flags & TRACE_FLAG_IRQS_OFF) ? 'd' :
>>  		bh_off ? 'b' :
>> -		(entry->flags & TRACE_FLAG_IRQS_NOSUPPORT) ? 'X' :
>> +		!IS_ENABLED(CONFIG_TRACE_IRQFLAGS_SUPPORT) ? 'X' :
>>  		'.';
>>
>> -	switch (entry->flags & (TRACE_FLAG_NEED_RESCHED |
>> +	switch (entry->flags & (TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_NEED_RESCHED_LAZY |
>>  				TRACE_FLAG_PREEMPT_RESCHED)) {
>> +	case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_NEED_RESCHED_LAZY | TRACE_FLAG_PREEMPT_RESCHED:
>> +		need_resched = 'B';
>> +		break;
>>  	case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_PREEMPT_RESCHED:
>>  		need_resched = 'N';
>>  		break;
>> +	case TRACE_FLAG_NEED_RESCHED_LAZY | TRACE_FLAG_PREEMPT_RESCHED:
>> +		need_resched = 'L';
>> +		break;
>> +	case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_NEED_RESCHED_LAZY:
>> +		need_resched = 'b';
>> +		break;
>>  	case TRACE_FLAG_NEED_RESCHED:
>>  		need_resched = 'n';
>>  		break;
>> +	case TRACE_FLAG_NEED_RESCHED_LAZY:
>> +		need_resched = 'l';
>> +		break;
>>  	case TRACE_FLAG_PREEMPT_RESCHED:
>>  		need_resched = 'p';
>>  		break;


--
ankur