linux-kernel - Re: [RFC PATCH 0/3] Rework CPU capacity asymmetry detection

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Date:   Wed, 21 Apr 2021 20:58:21 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Beata Michalska <beata.michalska@....com>,
        linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        corbet@....net, linux-doc@...r.kernel.org
Subject: Re: [RFC PATCH 0/3] Rework CPU capacity asymmetry detection

On 16/04/21 14:01, Beata Michalska wrote:
> Verified on (mostly):
>     - QEMU (version 4.2.1) with variants of possible asymmetric topologies
>       - machine: virt
>       - modifying the device-tree 'cpus' node for virt machine:
>
>       qemu-system-aarch64 -kernel $KERNEL_IMG
>           -drive format=qcow2,file=$IMAGE
>           -append 'root=/dev/vda earlycon console=ttyAMA0 sched_debug
>            loglevel=15 kmemleak=on' -m 2G  --nographic  -cpu cortex-a57
>           -machine virt -smp cores=6 -machine dumpdtb=$CUSTOM_DTB.dtb
>
>       $KERNEL_PATH/scripts/dtc/dtc -I dtb -O dts $CUSTOM_DTB.dts >
>       $CUSTOM_DTB.dtb
>
>       (modify the dts)
>
>       $KERNEL_PATH/scripts/dtc/dtc -I dts -O dtb $CUSTOM_DTB.dts >
>       $CUSTOM_DTB.dtb
>
>       qemu-system-aarch64 -kernel $KERNEL_IMG
>           -drive format=qcow2,file=$IMAGE
>           -append 'root=/dev/vda earlycon console=ttyAMA0 sched_debug
>            loglevel=15 kmemleak=on' -m 2G  --nographic  -cpu cortex-a57
>           -machine virt -smp cores=6 -machine dtb=$CUSTOM_DTB.dtb
>

Thanks to your QEMU wizardry, I've also tested this on a few funky
topologies such as:

  DIE [                     ]
  MC  [       ][            ]
       0  1  2  3  4  5  6  7
       L  L  M  L  L  M  B  B

and

  DIE [                ]
  MC  [          ][    ]
       0  1  2  3  4  5
       L  L  M  M  B  B

+ some hotplug ops, and the resulting SD_ flags all made sense to me.

Tested-by: Valentin Schneider <valentin.schneider@....com>

For patches 1, 3:
Reviewed-by: Valentin Schneider <valentin.schneider@....com>

>
> Beata Michalska (3):
>   sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL sched_domain flag
>   sched/topology: Rework CPU capacity asymmetry detection
>   sched/doc: Update the CPU capacity asymmetry bits
>
>  Documentation/scheduler/sched-capacity.rst |   6 +-
>  Documentation/scheduler/sched-energy.rst   |   2 +-
>  include/linux/sched/sd_flags.h             |  10 +
>  kernel/sched/topology.c                    | 339 +++++++++++++++++++++++++----
>  4 files changed, 314 insertions(+), 43 deletions(-)
>
> --
> 2.7.4