[PATCH 0/2] [tip: sched/core] sched: Disable PLACE_LAG and RUN_TO_PARITY and move them to sysctl

[Peter Zijlstra]

On Thu, Oct 17, 2024 at 12:19:58AM -0500, Cristian Prundeanu wrote:

> For example, running mysql+hammerdb results in a 12-17% throughput 

Gautham, is this a benchmark you're running?

> Testing combinations of available scheduler features showed that the 
> largest improvement (short of disabling all EEVDF features) came from 
> disabling both PLACE_LAG and RUN_TO_PARITY:

How does using SCHED_BATCH compare?

> While the long term approach is debugging and fixing the scheduler 
> behavior, algorithm changes to address performance issues of this nature 
> are specialized (and likely prolonged or open-ended) research. Until a 
> change is identified which fixes the performance degradation, in the 
> interest of a better out-of-the-box performance: (1) disable these 
> features by default, and (2) expose these values in sysctl instead of 
> debugfs, so they can be more easily persisted across reboots.

So disabling them by default will undoubtedly affect a ton of other
workloads. And sysctl is arguably more of an ABI than debugfs, which
doesn't really sound suitable for workaround.

And I don't see how adding a line to /etc/rc.local is harder than adding
a line to /etc/sysctl.conf