linux-kernel - 答复: [????] Re: divide error in x86 and cputime

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Message-ID: <42f5344b80e244278aaf49f112498e02@baidu.com>
Date: Tue, 8 Jul 2025 01:40:27 +0000
From: "Li,Rongqing" <lirongqing@...du.com>
To: Steven Rostedt <rostedt@...dmis.org>, Oleg Nesterov <oleg@...hat.com>
CC: Peter Zijlstra <peterz@...radead.org>, David Laight
	<david.laight.linux@...il.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "vschneid@...hat.com" <vschneid@...hat.com>,
	"mgorman@...e.de" <mgorman@...e.de>, "bsegall@...gle.com"
	<bsegall@...gle.com>, "dietmar.eggemann@....com" <dietmar.eggemann@....com>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"juri.lelli@...hat.com" <juri.lelli@...hat.com>, "mingo@...hat.com"
	<mingo@...hat.com>
Subject: 答复: [????] Re: divide error in x86 and cputime

> That would be:
> 
>                                    minutes    days
>                                       v        v
>   9223372036854775808 / 1000000000 / 60 / 60 / 24 / 365.25 = 292.27
>                            ^               ^         ^
>                         ns -> sec       hours       years
> 
> So the report says they have threads running for a very long time, it would still
> be 292 years of run time!

Utime/rtime is u64, it means overflow needs 292.27*2=584 year,

But with multiple thread, like 292 threads, it only need two years, it is a thread group total running time


void thread_group_cputime_adjusted(struct task_struct *p, u64 *ut, u64 *st)
{
    struct task_cputime cputime;

    thread_group_cputime(p, &cputime);
    cputime_adjust(&cputime, &p->signal->prev_cputime, ut, st);
}

-Li