linux-kernel - Re: [PATCH] sched/fair: fix pick_eevdf to always find the correct se

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Message-ID: <62ca6115-cf0d-427d-92c5-3539a361b476@samsung.com>
Date:   Fri, 6 Oct 2023 10:36:27 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Biju Das <biju.das.jz@...renesas.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     "bsegall@...gle.com" <bsegall@...gle.com>,
        "bristot@...hat.com" <bristot@...hat.com>,
        "chris.hyser@...cle.com" <chris.hyser@...cle.com>,
        "corbet@....net" <corbet@....net>,
        "dietmar.eggemann@....com" <dietmar.eggemann@....com>,
        "efault@....de" <efault@....de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "joel@...lfernandes.org" <joel@...lfernandes.org>,
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        "juri.lelli@...hat.com" <juri.lelli@...hat.com>,
        "kprateek.nayak@....com" <kprateek.nayak@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
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        <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH] sched/fair: fix pick_eevdf to always find the correct
 se

On 05.10.2023 17:08, Biju Das wrote:
> Hi Peter Zijlstra,
>
>> Subject: Re: [PATCH] sched/fair: fix pick_eevdf to always find the correct
>> se
>>
>> On Thu, Oct 05, 2023 at 07:31:34AM +0000, Biju Das wrote:
>>
>>> [   26.099203] EEVDF scheduling fail, picking leftmost
>> This, that the problem.. the rest is just noise because printk stinks.
>>
>> Weirdly have not seen that trigger, and I've been running with this patch
>> on for a few days now :/
> I agree Original issue is "EEVDF scheduling fail, picking leftmost"
> Which is triggering noisy lock warning messages during boot.
>
> 2 platforms are affected both ARM platforms(Renesas and Samsung)
> Maybe other platforms affected too.


Just to note, I've run into this issue on the QEmu's 'arm64/virt' 
platform, not on the Samsung specific hardware.


You can easily reproduce it with the following steps:

# make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- defconfig

# ./scripts/config -e PROVE_LOCKING -e DEBUG_ATOMIC_SLEEP -e PM_DEBUG -e 
PM_ADVANCED_DEBUG

# make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- olddefconfig Image.gz

# wget 
https://cloud.debian.org/images/cloud/buster/20230802-1460/debian-10-nocloud-arm64-20230802-1460.tar.xz

# tar xJfv debian-10-nocloud-arm64-20230802-1460.tar.xz


Then run QEmu a few times until you see the lockdep splat:

# qemu-system-aarch64 -serial stdio -kernel arch/arm64/boot/Image 
-append "console=ttyAMA0 root=/dev/vda1 rootwait" -M virt -cpu 
cortex-a57 -smp 2 -m 1024 -netdev user,id=user -device 
virtio-net-device,netdev=user -display none -device 
virtio-blk-device,drive=virtio-blk0 -drive 
file=disk.raw,id=virtio-blk0,if=none,format=raw


I have no idea if this is ARM64-specific anyhow, but this is how I 
reproduced it. I hope this guide helps fixing the bug!

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland