NACK/Cmnt [SRU][F][J][PATCH 0/1] ACPI: CPPC: Disable FIE if registers in PCC regions

[Stefan Bader]

On 19.10.22 00:13, Shiyou Huang wrote:
> Buglink: https://bugs.launchpad.net/ubuntu-realtime/+bug/1993326 
> <https://bugs.launchpad.net/ubuntu-realtime/+bug/1993326>
> 
> SRU Justification:
> 
> [Impact]
> With cppc_fie enabled, users can see 2% - 11% CPU overhead even when the system 
> is idle. On real time kernel, cppc_fie leads to higher latencies up to 120 
> microseconds.
> 
> The following patch:
> https://github.com/torvalds/linux/commit/ae2df912d1a557a3548be83da20851ac55f42ab3 <https://github.com/torvalds/linux/commit/ae2df912d1a557a3548be83da20851ac55f42ab3>
> fixes this issue by allowing users to disable cppc_fie at boot time.
> 
> [Test Case]
> Running 'cyclictest' on an 80-core arm system with the following command:
>   `sudo cyclictest -m -Sp90 -i200 -l100000 -h 400`
> 
> Without the patch, the max latency reported is 121 us while with the patch the 
> max latency is 20 us.
> 
> [Regression Potential]
> This patch only affects the aarch64 architecture and is limited to the 
> CPPC_CPUFREQ driver. Any regression is limited to this driver. From our testing, 
> we find that there are no regressions by this patch.
> 
> [Other Info]
> None
> 
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> 

Cover email and patch are not threaded. It is mot possible to keep things 
together in a sane manner. Also the patch itself does not show up for me. Please 
use a mailer that sticks to standards. And finally, I am not sure we can accept 
things which claim they are confidential... ;)

-Stefan

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