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SubjectRe: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling feature
On Wed, 26 Oct 2016, Peter Zijlstra wrote:
> On Wed, Oct 26, 2016 at 12:49:36PM +0200, Thomas Gleixner wrote:
>
> > > + /*
> > > + * ITMT capability automatically enables ITMT
> > > + * scheduling for small systems (single node).
> > > + */
> > > + if (topology_num_packages() == 1)
> > > + sysctl_sched_itmt_enabled = 1;
> >
> > I really hate this. This is policy and the kernel should not impose
> > policy. Why would I like to have this enforced on my single socket XEON
> > server?
>
> So this really wants to be enabled by default; otherwise nobody will use
> this, and it really does help single threaded workloads.

Fair enough. Then this wants to be documented.

> There were reservations on the multi-socket case of ITMT, maybe it would
> help to spell those out in great detail here. That is, have the comment
> explain the policy instead of simply stating what the code does (which
> is always bad comment policy, you can read the code just fine).

What is the objection for multi sockets? If it improves the behaviour then
why would this be a bad thing for multi sockets?

Thanks,

tglx

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