Re: [PATCH 2/2] x86/idle: use dynamic halt poll

From	Thomas Gleixner <tglx@linutronix.de>
Newsgroups	linux.kernel
Subject	Re: [PATCH 2/2] x86/idle: use dynamic halt poll
Date	2017-07-04 17:00 +0200
Message-ID	<tZxt0-1ij-11@gated-at.bofh.it> (permalink)
References	(6 earlier) <tWZ2q-1ch-13@gated-at.bofh.it> <tWZc5-1gg-5@gated-at.bofh.it> <tWZF9-1JQ-57@gated-at.bofh.it> <tZ5Q7-7za-25@gated-at.bofh.it> <tZwQi-Ro-19@gated-at.bofh.it>
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On Tue, 4 Jul 2017, Radim Krčmář wrote:
> I think there is a nicer solution to avoid the expensive timer rewrite:
> Linux uses one-shot APIC timers and getting the timer interrupt is about
> as expensive as programming the timer, so the guest can keep the timer
> armed, but not re-arm it after the expiration if the CPU is idle.

So much for the theory. The NOHZ logic has to reprogram the timer when the
next expiry is farther away than the next tick. Otherwise you wake up on
every idle entry once for nothing, which defeats the whole purpose of NOHZ
to not do that.

Thanks,

	tglx

Thread

Re: [PATCH 2/2] x86/idle: use dynamic halt poll Radim Krčmář <rkrcmar@redhat.com> - 2017-07-04 16:20 +0200
  Re: [PATCH 2/2] x86/idle: use dynamic halt poll Thomas Gleixner <tglx@linutronix.de> - 2017-07-04 17:00 +0200
  Re: [PATCH 2/2] x86/idle: use dynamic halt poll Yang Zhang <yang.zhang.wz@gmail.com> - 2017-07-13 14:00 +0200
    Re: [PATCH 2/2] x86/idle: use dynamic halt poll Alexander Graf <agraf@suse.de> - 2017-07-14 11:40 +0200
      Re: [PATCH 2/2] x86/idle: use dynamic halt poll Yang Zhang <yang.zhang.wz@gmail.com> - 2017-07-17 11:30 +0200
        Re: [PATCH 2/2] x86/idle: use dynamic halt poll Alexander Graf <agraf@suse.de> - 2017-07-17 12:00 +0200
          Re: [PATCH 2/2] x86/idle: use dynamic halt poll Yang Zhang <yang.zhang.wz@gmail.com> - 2017-07-17 15:00 +0200

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