linux-kernel - Re: [RFC 1/3] softirq: Use preempt_latency

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Message-ID: <20190529082945.GE2623@hirez.programming.kicks-ass.net>
Date:   Wed, 29 May 2019 10:29:45 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Daniel Bristot de Oliveira <bristot@...hat.com>
Cc:     linux-kernel@...r.kernel.org, williams@...hat.com,
        daniel@...stot.me, "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Yangtao Li <tiny.windzz@...il.com>,
        Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>
Subject: Re: [RFC 1/3] softirq: Use preempt_latency_stop/start to trace
 preemption

On Tue, May 28, 2019 at 05:16:22PM +0200, Daniel Bristot de Oliveira wrote:
> prempt_disable/enable tracepoints occurs only in the preemption
> enabled <-> disable transition. As preempt_latency_stop() and
> preempt_latency_start() already do this control, avoid code
> duplication by using these functions in the softirq code as well.
> 
> RFC: Should we move preempt_latency_start/preempt_latency_stop
> to a trace source file... or even a header?

Yeah, a header might not be a bad idea.

> @@ -130,12 +132,8 @@ void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
>  		trace_softirqs_off(ip);
>  	raw_local_irq_restore(flags);
>  
> -	if (preempt_count() == cnt) {
> -#ifdef CONFIG_DEBUG_PREEMPT
> -		current->preempt_disable_ip = get_lock_parent_ip();
> -#endif
> -		trace_preempt_off(CALLER_ADDR0, get_lock_parent_ip());
> -	}
> +	preempt_latency_start(cnt);
> +

I'm thinking we can do without that empty line.

>  }
>  EXPORT_SYMBOL(__local_bh_disable_ip);
>  #endif /* CONFIG_TRACE_IRQFLAGS */