linux-kernel - Re: nohz: Update tick instead of restarting tick in tick_nohz_idle

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Message-ID: <20201127121542.GA109224@lothringen>
Date:   Fri, 27 Nov 2020 13:15:42 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Yunfeng Ye <yeyunfeng@...wei.com>
Cc:     fweisbec@...il.com, tglx@...utronix.de, mingo@...nel.org,
        linux-kernel@...r.kernel.org, Shiyuan Hu <hushiyuan@...wei.com>,
        Hewenliang <hewenliang4@...wei.com>
Subject: Re: nohz: Update tick instead of restarting tick in
 tick_nohz_idle_exit()

On Mon, Nov 23, 2020 at 09:22:08PM +0800, Yunfeng Ye wrote:
> In realtime scenarios, the "nohz_full" parameter is configured. Tick
> interference is not expected when there is only one realtime thread.
> But when the idle thread is switched to the realtime thread, the tick
> timer is restarted always.
> 
> So on the nohz full mode, it is unnecessary to restart the tick timer
> when there is only one realtime thread. Adding can_stop_full_tick()
> before restarting the tick, if it return true, keep tick stopped.
> 
> Signed-off-by: Yunfeng Ye <yeyunfeng@...wei.com>

We can indeed stop the tick and avoid it to be re-armed needlessly at this
point.

I'm taking your patch, I may just edit it a little and resend it.

Thanks!