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List:       linux-rt-users
Subject:    Re: Disable lapic timer
From:       Sebastian Andrzej Siewior <bigeasy () linutronix ! de>
Date:       2017-01-25 17:12:33
Message-ID: 20170125171233.i6lc5ttshd2nftxj () linutronix ! de
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On 2016-12-22 14:36:03 [+0100], Federico Reghenzani wrote:
> I found this very old topic
> 
> https://www.spinics.net/lists/linux-rt-users/msg05422.html
> 
> is there any update on this? I want to disable the APIC timer in order
> to increase the determinism of my system, but I'm not sure if this is
> possible without editing the kernel source code.
> 
> On my machine smp_apic_timer_interrupt takes 2-3 us, I know this is
> already low, but it's actually the only "frequent" latency that I have
> on the isolated cpu.

You need a timer for each active CPU that participates in the system.
The timer interrupt which comes each tick can't be disabled. You can
look at NO_HZ_FULL where you can have an isolated CPU and as long as you
don't go into kernel, you shouldn't see the timer interrupt very often.

> Thank you,
> Federico Reghenzani

Sebastian
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