nohz

note

1. nohz 作为替代 period tick的产物，其依赖什么

   • timer: oneshot timer device

     • 我们可以在很多代码角落找到这一证据

       • tick_check_new_device(): prefer one shot capable devices

     • why

       无论是因为nohz的作用就是替代周期性的tick，所以需要一个oneshot timer 来设置下次要到期的timer.

2. nohz 和hrtimer的关系

   • nohz 和 hrtimer 两者都需要高精度timer source， 所以两者是竞争关系， 为了解决这个问题，在enable hrtimer的情况下, tick-sched内置的timer使用 hrtimer， 而hrtimer则直接操控tick-device -- (tick_program_event)

commit

• High resolution timer / dynamic tick update -- (first instrucduce)

  • https://lore.kernel.org/all/[e-mail]/

  • 950f4427c2ddc921164088a20f01304cf231437c - 289f480af87e45f7a6de6ba9b4c061c2e259fe98

    • Thomas Gleixner

    • 2007-02-16

• nohz: Basic full dynticks interface

  • https://lore.kernel.org/all/[e-mail]/

  • https://lore.kernel.org/all/[e-mail]/

  • a831881be220358a1d28c5d95d69449fb6d623ca

    • Frederic Weisbecker [e-mail]

    • 2012-02-18

  • 1c20091e77fc5a9b7d7d905176443b4822a23cdb

    • nohz: Wake up full dynticks CPUs when a timer gets enqueued

  • 1a55af2e45cc sched: Update rq clock earlier in unthrottle_cfs_rq

  • 1ad4ec0dc740 sched: Update rq clock before calling check_preempt_curr()

  • 71b1da46ff70 sched: Update rq clock before setting fair group shares

  • 77bd39702f0b sched: Update rq clock before migrating tasks out of dying CPU

• Allow CPU0 to be nohz full

  • https://lore.kernel.org/all/[e-mail]/

  • 08ae95f4fd3b38b257f5dc7e6507e071c27ba0d5

    • Nicholas Piggin

    • 2019-04-11

other

https://events.linuxfoundation.org/wp-content/uploads/2024/02/Joel-Fernandes-Mentorship-Webinar-The-Ticking-Beast-LF-webinar-Feb-22nd-2024-public-copy.pdf

timer

https://wiki.osdev.org/Timer_Interrupt_Sources

RTC

https://wiki.osdev.org/Timer_Interrupt_Sources#Local_APIC_timer_(newer,_with_TSC_deadline_mode)

https://ieeexplore.ieee.org/document/4685768

https://cwiki.apache.org/confluence/display/NUTTX/Power+Management+-+Final+Report

https://www.codingshuttle.com/blogs/operating-systems-in-one-shot/

https://lore.kernel.org/all/[e-mail]/