linux-kernel - Re: [RFC PATCH v4 00/19] Core scheduling v4

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Date:   Thu, 31 Oct 2019 14:42:37 -0400
From:   Phil Auld <pauld@...hat.com>
To:     Vineeth Remanan Pillai <vpillai@...italocean.com>
Cc:     Nishanth Aravamudan <naravamudan@...italocean.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>, mingo@...nel.org,
        tglx@...utronix.de, pjt@...gle.com, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org, Dario Faggioli <dfaggioli@...e.com>,
        fweisbec@...il.com, keescook@...omium.org, kerrnel@...gle.com,
        Aaron Lu <aaron.lwe@...il.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [RFC PATCH v4 00/19] Core scheduling v4

Hi Vineeth,

On Wed, Oct 30, 2019 at 06:33:13PM +0000 Vineeth Remanan Pillai wrote:
> Fourth iteration of the Core-Scheduling feature.
> 
> This version was aiming mostly at addressing the vruntime comparison
> issues with v3. The main issue seen in v3 was the starvation of
> interactive tasks when competing with cpu intensive tasks. This issue
> is mitigated to a large extent.
> 
> We have tested and verified that incompatible processes are not
> selected during schedule. In terms of performance, the impact
> depends on the workload:
> - on CPU intensive applications that use all the logical CPUs with
>   SMT enabled, enabling core scheduling performs better than nosmt.
> - on mixed workloads with considerable io compared to cpu usage,
>   nosmt seems to perform better than core scheduling.
> 
> v4 is rebased on top of 5.3.5(dc073f193b70):
> https://github.com/digitalocean/linux-coresched/tree/coresched/v4-v5.3.5
> 
> Changes in v4
> -------------
> - Implement a core wide min_vruntime for vruntime comparison of tasks
>   across cpus in a core.
> - Fixes a typo bug in setting the forced_idle cpu.
> 
> Changes in v3
> -------------
> - Fixes the issue of sibling picking up an incompatible task
>   - Aaron Lu
>   - Vineeth Pillai
>   - Julien Desfossez
> - Fixes the issue of starving threads due to forced idle
>   - Peter Zijlstra
> - Fixes the refcounting issue when deleting a cgroup with tag
>   - Julien Desfossez
> - Fixes a crash during cpu offline/online with coresched enabled
>   - Vineeth Pillai
> - Fixes a comparison logic issue in sched_core_find
>   - Aaron Lu
> 
> Changes in v2
> -------------
> - Fixes for couple of NULL pointer dereference crashes
>   - Subhra Mazumdar
>   - Tim Chen
> - Improves priority comparison logic for process in different cpus
>   - Peter Zijlstra
>   - Aaron Lu
> - Fixes a hard lockup in rq locking
>   - Vineeth Pillai
>   - Julien Desfossez
> - Fixes a performance issue seen on IO heavy workloads
>   - Vineeth Pillai
>   - Julien Desfossez
> - Fix for 32bit build
>   - Aubrey Li
> 
> TODO
> ----
> - Decide on the API for exposing the feature to userland
> - Investigate the source of the overhead even when no tasks are tagged:
>   https://lkml.org/lkml/2019/10/29/242
> - Investigate the performance scaling issue when we have a high number of
>   tagged threads: https://lkml.org/lkml/2019/10/29/248
> - Try to optimize the performance for IO-demanding applications:
>   https://lkml.org/lkml/2019/10/29/261
> 
> ---
> 
> Aaron Lu (3):
>   sched/fair: wrapper for cfs_rq->min_vruntime
>   sched/fair: core wide vruntime comparison
>   sched/fair : Wake up forced idle siblings if needed
> 
> Peter Zijlstra (16):
>   stop_machine: Fix stop_cpus_in_progress ordering
>   sched: Fix kerneldoc comment for ia64_set_curr_task
>   sched: Wrap rq::lock access
>   sched/{rt,deadline}: Fix set_next_task vs pick_next_task
>   sched: Add task_struct pointer to sched_class::set_curr_task
>   sched/fair: Export newidle_balance()
>   sched: Allow put_prev_task() to drop rq->lock
>   sched: Rework pick_next_task() slow-path
>   sched: Introduce sched_class::pick_task()
>   sched: Core-wide rq->lock
>   sched: Basic tracking of matching tasks
>   sched: A quick and dirty cgroup tagging interface
>   sched: Add core wide task selection and scheduling.
>   sched/fair: Add a few assertions
>   sched: Trivial forced-newidle balancer
>   sched: Debug bits...
> 
>  include/linux/sched.h    |   9 +-
>  kernel/Kconfig.preempt   |   6 +
>  kernel/sched/core.c      | 847 +++++++++++++++++++++++++++++++++++++--
>  kernel/sched/cpuacct.c   |  12 +-
>  kernel/sched/deadline.c  |  99 +++--
>  kernel/sched/debug.c     |   4 +-
>  kernel/sched/fair.c      | 346 +++++++++++-----
>  kernel/sched/idle.c      |  42 +-
>  kernel/sched/pelt.h      |   2 +-
>  kernel/sched/rt.c        |  96 ++---
>  kernel/sched/sched.h     | 246 +++++++++---
>  kernel/sched/stop_task.c |  35 +-
>  kernel/sched/topology.c  |   4 +-
>  kernel/stop_machine.c    |   2 +
>  14 files changed, 1399 insertions(+), 351 deletions(-)
> 
> -- 
> 2.17.1
> 

Unless I'm mistaken 7 of the first 8 of these went into sched/core
and are now in linux (from v5.4-rc1). It may make sense to rebase on 
that and simplify the series.


Cheers,
Phil
--