• Johannes Weiner's avatar
    psi: pressure stall information for CPU, memory, and IO · eb414681
    Johannes Weiner authored
    When systems are overcommitted and resources become contended, it's hard
    to tell exactly the impact this has on workload productivity, or how close
    the system is to lockups and OOM kills.  In particular, when machines work
    multiple jobs concurrently, the impact of overcommit in terms of latency
    and throughput on the individual job can be enormous.
    
    In order to maximize hardware utilization without sacrificing individual
    job health or risk complete machine lockups, this patch implements a way
    to quantify resource pressure in the system.
    
    A kernel built with CONFIG_PSI=y creates files in /proc/pressure/ that
    expose the percentage of time the system is stalled on CPU, memory, or IO,
    respectively.  Stall states are aggregate versions of the per-task delay
    accounting delays:
    
           cpu: some tasks are runnable but not executing on a CPU
           memory: tasks are reclaiming, or waiting for swapin or thrashing cache
           io: tasks are waiting for io completions
    
    These percentages of walltime can be thought of as pressure percentages,
    and they give a general sense of system health and productivity loss
    incurred by resource overcommit.  They can also indicate when the system
    is approaching lockup scenarios and OOMs.
    
    To do this, psi keeps track of the task states associated with each CPU
    and samples the time they spend in stall states.  Every 2 seconds, the
    samples are averaged across CPUs - weighted by the CPUs' non-idle time to
    eliminate artifacts from unused CPUs - and translated into percentages of
    walltime.  A running average of those percentages is maintained over 10s,
    1m, and 5m periods (similar to the loadaverage).
    
    [hannes@cmpxchg.org: doc fixlet, per Randy]
      Link: http://lkml.kernel.org/r/20180828205625.GA14030@cmpxchg.org
    [hannes@cmpxchg.org: code optimization]
      Link: http://lkml.kernel.org/r/20180907175015.GA8479@cmpxchg.org
    [hannes@cmpxchg.org: rename psi_clock() to psi_update_work(), per Peter]
      Link: http://lkml.kernel.org/r/20180907145404.GB11088@cmpxchg.org
    [hannes@cmpxchg.org: fix build]
      Link: http://lkml.kernel.org/r/20180913014222.GA2370@cmpxchg.org
    Link: http://lkml.kernel.org/r/20180828172258.3185-9-hannes@cmpxchg.orgSigned-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
    Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Tested-by: default avatarDaniel Drake <drake@endlessm.com>
    Tested-by: default avatarSuren Baghdasaryan <surenb@google.com>
    Cc: Christopher Lameter <cl@linux.com>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Johannes Weiner <jweiner@fb.com>
    Cc: Mike Galbraith <efault@gmx.de>
    Cc: Peter Enderborg <peter.enderborg@sony.com>
    Cc: Randy Dunlap <rdunlap@infradead.org>
    Cc: Shakeel Butt <shakeelb@google.com>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Vinayak Menon <vinmenon@codeaurora.org>
    Cc: Randy Dunlap <rdunlap@infradead.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    eb414681
psi_types.h 1.92 KB