Re: [PATCH v2 0/4] sched/rt: mitigate root_domain cache line contention

[Peter Zijlstra]

On Mon, Jul 21, 2025 at 02:10:22PM +0800, Pan Deng wrote:
> When running multi-instance FFmpeg workload in cloud environment,
> cache line contention is severe during the access to root_domain data
> structures, which significantly degrades performance.
> 
> The SUT is a 2-socket machine with 240 physical cores and 480 logical

What's a SUT?

> CPUs. 60 FFmpeg instances are launched, each pinned to 4 physical cores
> (8 logical CPUs) for transcoding tasks. Sub-threads use RT priority 99
> with FIFO scheduling. FPS(frame per second) is used as score.

So I think we can do some of this, but that workload is hilariously
poorly configured.

You're pinning things but not partitioning, why?  If you would have
created 60 partitions, one for each FFmpeg thingy, then you wouldn't
have needed any of this.

You're running at FIFO99 (IOW prio-0) and then claiming prio-0 is used
more heavily than others... will d0h.  What priority assignment scheme
led to this? Is there a sensible reason these must be 99?