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

[Peter Zijlstra]

On Fri, Mar 20, 2026 at 10:59:55AM +0100, Peter Zijlstra wrote:
> 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?
> 

Also, you failed the most basic of tasks, Cc all the relevant people. I
would've hoped at least some of the 'reviewer' you had would've told you
about that.

Notably, Steve is the one that often looks after this RT stuff.