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From: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>,
	Stephen Boyd <sboyd@kernel.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] timer: Use static_branch_likely() for timers_nohz_active
Date: Fri, 20 Aug 2021 18:18:14 +0800	[thread overview]
Message-ID: <20210820181814.2761b051@xhacker.debian> (raw)
In-Reply-To: <87im0dqohb.ffs@tglx>

On Tue, 10 Aug 2021 18:00:16 +0200 Thomas Gleixner wrote:

> 
> 
> Jisheng,

Hi Thomas,

> 
> On Thu, Jun 24 2021 at 16:32, Jisheng Zhang wrote:
> 
> > The static key timers_nohz_active is likely to be true, so use
> > static_branch_likely() to reflect this fact.  
> 
> you still lack any justification for your statement that NOHZ active is
> likely.

This patch only affects NO_HZ_COMMON=y code path which is enabled if either
NO_HZ_IDLE or NO_HZ_FULL = y.
Per my understanding, when the system has oneshot tick device, NOHZ active
is likely true. After going through drivers/clocksource/*, I found there are
about 86 drivers, 69(occupies 80%) of which support CLOCK_EVT_FEAT_ONESHOT.
Then I browsed apic, hpet and xen timer source code in x86 directory, they
all support oneshot feature.

I'm not sure whether I misunderstood the code or not.

Thanks

> 
> It might be likely for your system, but is this true in general?
> 



      reply	other threads:[~2021-08-20 10:18 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-24  8:32 [PATCH v2] timer: Use static_branch_likely() for timers_nohz_active Jisheng Zhang
2021-08-10 16:00 ` Thomas Gleixner
2021-08-20 10:18   ` Jisheng Zhang [this message]

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