linux-kernel - Re: [PATCH 21/23] y2038: itimer: change implementation to timespec64

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Message-ID: <alpine.DEB.2.21.1911132306070.2507@nanos.tec.linutronix.de>
Date:   Wed, 13 Nov 2019 23:28:47 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Arnd Bergmann <arnd@...db.de>
cc:     y2038@...ts.linaro.org, Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Frederic Weisbecker <frederic@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 21/23] y2038: itimer: change implementation to
 timespec64

On Fri, 8 Nov 2019, Arnd Bergmann wrote:
>  TRACE_EVENT(itimer_state,
>  
> -	TP_PROTO(int which, const struct itimerval *const value,
> +	TP_PROTO(int which, const struct itimerspec64 *const value,
>  		 unsigned long long expires),
>  
>  	TP_ARGS(which, value, expires),
> @@ -321,12 +321,12 @@ TRACE_EVENT(itimer_state,
>  		__entry->which		= which;
>  		__entry->expires	= expires;
>  		__entry->value_sec	= value->it_value.tv_sec;
> -		__entry->value_usec	= value->it_value.tv_usec;
> +		__entry->value_usec	= value->it_value.tv_nsec / NSEC_PER_USEC;
>  		__entry->interval_sec	= value->it_interval.tv_sec;
> -		__entry->interval_usec	= value->it_interval.tv_usec;
> +		__entry->interval_usec	= value->it_interval.tv_nsec / NSEC_PER_USEC;

Hmm, having a division in a tracepoint is clearly suboptimal.

>  	),
>  
> -	TP_printk("which=%d expires=%llu it_value=%ld.%ld it_interval=%ld.%ld",
> +	TP_printk("which=%d expires=%llu it_value=%ld.%06ld it_interval=%ld.%06ld",

We print only 6 digits after the . so that would be even correct w/o a
division. But it probably does not matter much.

> @@ -197,19 +207,13 @@ static void set_cpu_itimer(struct task_struct *tsk, unsigned int clock_id,
>  #define timeval_valid(t) \
>  	(((t)->tv_sec >= 0) && (((unsigned long) (t)->tv_usec) < USEC_PER_SEC))

Hrm, why do we have yet another incarnation of timeval_valid()? Can we
please have only one (the inline version)?

Thanks,

	tglx