linux-kernel - Re: [PATCH v2] sched/debug: Put sched/domains files under the verbose flag

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Message-ID: <Y+x1sO2zclDex3UI@li-05afa54c-330e-11b2-a85c-e3f3aa0db1e9.ibm.com>
Date:   Wed, 15 Feb 2023 11:33:28 +0530
From:   Vishal Chourasia <vishalc@...ux.vnet.ibm.com>
To:     Phil Auld <pauld@...hat.com>
Cc:     linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
        mingo@...hat.com, peterz@...radead.org, ritesh.list@...il.com,
        srikar@...ux.vnet.ibm.com, sshegde@...ux.ibm.com,
        vincent.guittot@...aro.org, vschneid@...hat.com
Subject: Re: [PATCH v2] sched/debug: Put sched/domains files under the
 verbose flag

On Fri, Jan 20, 2023 at 11:33:30AM -0500, Phil Auld wrote:
> The debug files under sched/domains can take a long time to regenerate,
> especially when updates are done one at a time. Move these files under
> the sched verbose debug flag. Allow changes to verbose to trigger
> generation of the files. This lets a user batch the updates but still
> have the information available.  The detailed topology printk messages
> are also under verbose.
> 
> Discussion that lead to this approach can be found in the link below.
> 
> Simplified code to maintain use of debugfs bool routines suggested by
> Michael Ellerman <mpe@...erman.id.au>.
> 
> Signed-off-by: Phil Auld <pauld@...hat.com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
> Cc: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
> Cc: Valentin Schneider <vschneid@...hat.com>
> Cc: Vishal Chourasia <vishalc@...ux.vnet.ibm.com>
> Cc: Vincent Guittot <vincent.guittot@...aro.org>
> Link: https://lore.kernel.org/all/Y01UWQL2y2r69sBX@li-05afa54c-330e-11b2-a85c-e3f3aa0db1e9.ibm.com/
> ---
> 
>  v2: fix comment typo and use cpumask_empty()
> 
>  kernel/sched/debug.c | 52 +++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 49 insertions(+), 3 deletions(-)

Thanks for the Patch.

Tested-by: Vishal Chourasia <vishalc@...ux.vnet.ibm.com>

Base Tag       : v6.2-rc8  
Patch          : [V2] sched/debug: Put sched/domains files under the verbose flag


# time ppc64_cpu --smt=off   | When kernel is built  
                             | with the patch, time to
real    17m54.246s           | smt=off is 17m54s.    
user    0m0.013s             |
sys     0m4.661s             |

System Configuration:

Architecture    : ppc64le
CPUS            : 1600
Machine         : Power10
Thread per core : 8
Sockets         : 15

- debug files are not created for the case where kernel command line string
  lacks sched_verbose parameter.
- When sched_verbose is passed as kernel commandline parameter, kernel exports
  /sys/kernel/debug/sched/verbose file which controls creation of the debug
  files.
  + setting Y/N to this file enables/disables creation of debug files during CPU
    hotplug operation.

Below is the table listing time taken to perform smt=off operation under
different settings.

+--------------------------+---------------+---------+------------+
| kernel                   | sched_verbose | verbose | time       |
+--------------------------+---------------+---------+------------+
| 6.2.0-rc8-patch-applied+ | YES           | N       | 16m58.196s |
| 6.2.0-rc8-patch-applied+ | YES           | Y       | 33m21.774s |
| 6.2.0-rc8-patch-applied+ | NO            | NA      | 17m54.246s |
| 6.2.0-rc8                | NO            | NA      | 30m11.344s |
+--------------------------+---------------+---------+------------+

-- vishal.c
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