Re: [PATCH 2/6] sched: tagging interface for core scheduling

[Peter Zijlstra]

On Mon, Mar 22, 2021 at 01:57:48PM -0400, Chris Hyser wrote:
> On 3/20/21 11:46 AM, Peter Zijlstra wrote:
> > On Fri, Mar 19, 2021 at 04:32:49PM -0400, Joel Fernandes (Google) wrote:
> > > From: Josh Don <joshdon@xxxxxxxxxx>
> > > 
> > > Adds per-task and per-cgroup interfaces for specifying which tasks can
> > > co-execute on adjacent SMT hyperthreads via core scheduling.
> > > 
> > > The per-task interface hooks are implemented here, but are not currently
> > > used. The following patch adds a prctl interface which then takes
> > > advantage of these.
> > > 
> > > The cgroup interface can be used to toggle a unique cookie value for all
> > > descendent tasks, preventing these tasks from sharing with any others.
> > > See Documentation/admin-guide/hw-vuln/core-scheduling.rst for a full
> > > rundown.
> > > 
> > > One important property of this interface is that neither the per-task
> > > nor the per-cgroup setting overrides the other. For example, if two
> > > tasks are in different cgroups, and one or both of the cgroups is tagged
> > > using the per-cgroup interface, then these tasks cannot share, even if
> > > they use the per-task interface to attempt to share with one another.
> > > 
> > > The above is implemented by making the overall core scheduling cookie a
> > > compound structure, containing both a task-level cookie and a
> > > group-level cookie. Two tasks will only be allowed to share if all
> > > fields of their respective cookies match.
> > > 
> > > Core scheduler has extra overhead.  Enable it only for machines with
> > > more than one SMT hardware thread.
> > 
> > Oh man.. I'd soooo hoped to first see the simple task interface and then
> > see the cgroup patch on top of that... I'll see if I can flip them
> > myself (on monday).
> 
> Peter, given we need to rebase this and we have some cleanup, we can go
> ahead and flip the order if you have not yet done so yet.

I didn't get around to it yet :/ So yes, please! Also can you then split
the selftest thingies?