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[Joseph Salisbury <joseph.salisbury@xxxxxxxxxxxxx>]

Did this issue start happening after an update/upgrade? Was there a
kernel version where you were not having this particular problem? This
will help determine if the problem you are seeing is the result of a
regression, and when this regression was introduced.   If this is a
regression, we can perform a kernel bisect to identify the commit that
introduced the problem.


** Changed in: linux (Ubuntu)
   Importance: Undecided => Medium

** Changed in: linux (Ubuntu)
       Status: Confirmed => Incomplete

** Tags added: kernel-da-key

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https://bugs.launchpad.net/bugs/1587265

Title:
  ubuntu not work with tickless kernel boot option

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  For redhat, we have such guide like 
  https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/pdf/Performance_Tuning_Guide/Red_Hat_Enterprise_Linux-7-Performance_Tuning_Guide-en-US.pdf

  and for tickless kernel, (use dynamic tickless ways)

  1. config grub with following cmdline

  $ cat /etc/default/grub 
  # If you change this file, run 'update-grub' afterwards to update
  # /boot/grub/grub.cfg.
  # For full documentation of the options in this file, see:
  #   info -f grub -n 'Simple configuration'

  GRUB_DEFAULT=0
  GRUB_HIDDEN_TIMEOUT=0
  GRUB_HIDDEN_TIMEOUT_QUIET=true
  GRUB_TIMEOUT=10
  GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
  GRUB_CMDLINE_LINUX_DEFAULT="quiet splash isolcpus=1-2 nohz_full=1-2"
  GRUB_CMDLINE_LINUX=""


  I used nohz_full here, and it is CPU 1, 2 here.

  2. update-grub after that.
  3. Then reboot system

  4. execute following 
  $ sudo perf stat  -C  1  -e irq_vectors:local_timer_entry taskset -c 1 stress -t 1 -c 1
  stress: info: [3869] dispatching hogs: 1 cpu, 0 io, 0 vm, 0 hdd
  stress: info: [3869] successful run completed in 1s

   Performance counter stats for 'CPU(s) 1':

                 252      irq_vectors:local_timer_entry

         1.001491203 seconds time elapsed

  
  It always 252, (the default 250 HZ), seems tickless kernel option not have any effect, whether config it or not, both have same results.

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