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From: Wanpeng Li <kernellwp@gmail.com>
Date: Tue, 9 Aug 2016 11:59:07 +0800
Message-ID: <CANRm+CyYHLaihuk+ckQg42-Lo_3vFHaS8gU=GmXh8Rfq5mMpaA@mail.gmail.com>
Subject: Re: [PATCH 1/5] sched,time: Count actually elapsed irq & softirq time
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Rik van Riel <riel@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Wanpeng Li <wanpeng.li@hotmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Radim Krcmar <rkrcmar@redhat.com>, Mike Galbraith <efault@gmx.de>
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Hi Rik,
2016-07-13 22:50 GMT+08:00 Frederic Weisbecker <fweisbec@gmail.com>:
> From: Rik van Riel <riel@redhat.com>
>
> Currently, if there was any irq or softirq time during 'ticks'
> jiffies, the entire period will be accounted as irq or softirq
> time.
>
> This is inaccurate if only a subset of the time was actually spent
> handling irqs, and could conceivably mis-count all of the ticks during
> a period as irq time, when there was some irq and some softirq time.
>
> This can actually happen when irqtime_account_process_tick is called
> from account_idle_ticks, which can pass a larger number of ticks down
> all at once.
>
> Fix this by changing irqtime_account_hi_update, irqtime_account_si_update,
> and steal_account_process_ticks to work with cputime_t time units, and
> return the amount of time spent in each mode.

Do we need to minus st cputime from idle cputime in
account_idle_ticks() when noirqtime is true? I try to add this logic
w/ noirqtime and idle=poll boot parameter for a full dynticks guest,
however, there is no difference, where I miss?

Regards,
Wanpeng Li