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Date: Tue, 15 Jun 2021 08:01:15 +0200
From: Greg KH <gregkh@linuxfoundation.org>
To: Adam Edge <baronedge@protonmail.com>
Cc: "stable@vger.kernel.org" <stable@vger.kernel.org>,
	"regressions@lists.linux.dev" <regressions@lists.linux.dev>
Subject: Re: Regression after 5.7.19 causing major freezes on CPU loads
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On Mon, Jun 14, 2021 at 07:21:55PM +0000, Adam Edge wrote:
> Hello,
> 
> After I've upgraded from 5.7.11 (didn't have access to this machine for
> about 10 months) to 5.12.10, I've noticed that anytime I used all my
> cores to, for example, compile a project, the system would degrade
> significantly in performance and applications would start to stutter.
> Compiles are also about 3-4x slower on kernels with the regression vs.
> without. After debugging this for the past 24 hours or so, I've narrowed
> it down to a change between 5.7.19 and 5.8.1. Sadly, bisect does not
> help, because trying to run any of the 5.8 RC kernels causes the kernel
> to be stuck before init, without any apparent errors on the screen (and
> I don't have a serial cable to dump the kernel output to). I'm listing
> all the information I know and my system information below.
> 
> Reproduction steps (dunno if this helps, but):
> 1. Boot with kernel with the regression
> 2. Do something that uses all cores, like compiling the Linux kernel
> 3. Observe long compile times and stuttering applications (which doesn't
> happen even on full load with a working kernel)
> 
> Regression between kernel versions:
> 5.7 - working
> 5.7.11 - working
> 5.7.19 - working
> 5.8.1 - broken
> 5.8.18 - broken
> 5.12.10 - broken
> 8ecfa36cd4db3275bf3b6c6f32c7e3c6bb537de2 (master on 2021-06-13) - broken

Can you use 'git bisect' to track down the commit that caused the
problem?

thanks,

greg k-h