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2021-1-11 Meeting Meeting notes

2021-1-11 Meeting Meeting notes

Owned by Mike Holmes
Last updated: Jan 11, 2021

Meeting Details

Topic: linaro-open-discussion meeting
Time: Jan 11 , 2020 10.00 AM London

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https://linaro-org.zoom.us/j/4417312160

Meeting ID: 441 731 2160
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Meeting ID: 441 731 2160
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Attendees

  • Mike
  • Tim Chen ( Intel )
  • Zhangfei Gao (Hisilicon LT)
  • Shameerali KT
  • Jammy
  • Mortenson (Arm)
  • Lorenzo (Arm)
  • Dietmar (Arm)
  • Valentine (Arm)
  • James Morse ()
  • Jonathan Cameron (Huawei)
  • Vincent 
  • Barry Song (Huawei)
  • Chris Redpath (arm)
  • Sudeep Holla (arm)
  • Ulf 
  • Bill F
  • Loic Pallardy (ST)
  • Guodong Xu (Hisilicon LT)
  • Salil Mehta (Huawei)
  • Mattias Brugger (SUSE ?)
  • ZengTao  ( ? )
  • wanghuiqiang (Huawei)

Agenda

Confirmed topics

  • Lorenzo Pieralisi : Arm : Scheduler topology: cluster scheduler awareness - 
  • Lorenzo Pieralisi : Arm : ACPI CPU hotplug
  • AOB 
    • Jonathon

Meeting notes 

  • Lorenzo Pieralisi : Arm : Scheduler topology: cluster scheduler awareness
    • Song Bao Hua
      • talking to slides
      • Better performance in single cluster vs multiple - lead to the investigation, used Jonathon patch to test Linux scheduler.
      • hackbench better with select_idle_sibling.  it collates the waking up of a cluster
    • Vincent, Morten there are multiple topics
      • Morten
        • how to get information
        • scheduling policy - this first
        • Need a wider discussion. Made some comments on Friday
      • Vincent 
        • Scheduler policy - adding scheduling level,  I don't see any pushback and there is perf improvement
        • Sometimes you want to spread and other times cluster - HB there are 40 threads, there are few idle states, it is about spreading tasks. Patches should fit on Peter's wakeup patches, NUMA scheduling will be most challenging.
        • Dietmar - will this scan and fall back to standard LNC? (V3)  VG: cant loop, but in a new approach, it is OK as you hit each CPU only once.
        • Morten, when is it good to pack vs spread them?  What is the measure to understand which approach to take.  And example two tasks with a lot of shared data will be a problem.
        • Vincent, need to look at previous CPU being idle. migrating may happen to move tasks from one cluster to another, need to complete task before load balance takes effect
        • JC:  if this is spread across NUMA nodes we have many more than 40 CPUs
          • VG: There will not be any on the longer one.
        • DE: we don't have an example where we chose a policy based on the workload
      • Lorenzo - we have covered topic one of this 35 mins spent, let's move to the list where we can
      • Tim Chen
        • X86 will also need this concept
        • could have tasks that share memory without a wakeup relationship
        • SBH - userspace may need to provide information 
      • JC: we can gather the info even if it is not accurate initially, we perhaps need to gather data separately
        • X86 does not use PPTT - but there are extra levels of topology information
        • TC we are using L2 
        • JC we don't have a way to represent L3 tag cache
        • Die is no available to userspace
        • Any concerns on extra complexity?
        • LP: userspace should be architectural - JC: sort of agree, with generic naming, MR: why don't you just dump PPTT, JC: kernel is not always enabled to get dump MC: we could patch this.
      • SBH will send a V4 at this time


LP - AOB

  • Lorenzo Pieralisi : Arm : ACPI CPU hotplug
    • Progress with discussions - 2  PSCI solutions, QEmu changes or use ACPI as it is in X86 world
    • Working inside Arm as things firm up
    • For hotplug in a VM, suspect it relies on userspace - is actually align in userspace,   Salil Mehta that is correct. 
      • SM: at QEMU level you need an event, LP: in guest, there is something to be done, SM yes, we are using sysfs - Justin He was using VSOCK event -, we are doing it manually for testing
      • RMR - we sorted it out, need to get it done specs will follow
  • JC - don't re-enumerate PCI - discussion with Jean-Phillip

Action items

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