lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:   Wed, 5 Sep 2018 23:06:38 -0700
From:   Dietmar Eggemann <>
To:     Quentin Perret <>,,,,
Subject: Re: [PATCH v6 07/14] sched/topology: Introduce sched_energy_present
 static key

On 08/20/2018 02:44 AM, Quentin Perret wrote:
> In order to ensure a minimal performance impact on non-energy-aware
> systems, introduce a static_key guarding the access to Energy-Aware
> Scheduling (EAS) code.
> The static key is set iff all the following conditions are met for at
> least one root domain:
>    1. all online CPUs of the root domain are covered by the Energy
>       Model (EM);
>    2. the complexity of the root domain's EM is low enough to keep
>       scheduling overheads low;
>    3. the root domain has an asymmetric CPU capacity topology (detected
>       by looking for the SD_ASYM_CPUCAPACITY flag in the sched_domain
>       hierarchy).

This is pretty much the list (+ is schedutil running) of conditions to 
set rd->pd != NULL in build_perf_domains().

So when testing 'static_branch_unlikely(&sched_energy_present) && 
rcu_dereference(rd->pd)' don't you test two times the same thing?

Also, if let's say somebody wants to run another EM user (e.g. a thermal 
governor, like IPA) but not EAS on a asymmetric CPU capacity system. 
This can't be achieved with the current static branch approach

So what about using a (disabled by default ?) sched_feature + rd->pd != 
NULL instead?


Powered by blists - more mailing lists