Subject: Re: [v5] powerpc/topology: Get topology for shared processors at boot

From: Srikar Dronamraju <[email-masked]>
Date: Tue, 21 Aug 2018 19:05:42 -0700

* Michael Ellerman <[email-masked]> [2018-08-21 20:35:23]:

> On Fri, 2018-08-17 at 14:54:39 UTC, Srikar Dronamraju wrote:
> > On a shared lpar, Phyp will not update the cpu associativity at boot
> > time. Just after the boot system does recognize itself as a shared lpar and
> > trigger a request for correct cpu associativity. But by then the scheduler
> > would have already created/destroyed its sched domains.
> > 
> > This causes
> > - Broken load balance across Nodes causing islands of cores.
> > - Performance degradation esp if the system is lightly loaded
> > - dmesg to wrongly report all cpus to be in Node 0.
> > - Messages in dmesg saying borken topology.
> > - With commit 051f3ca02e46 ("sched/topology: Introduce NUMA identity
> >   node sched domain"), can cause rcu stalls at boot up.
> > 
> > 
> > Previous attempt to solve this problem
> > https://patchwork.ozlabs.org/patch/530090/
> > 
> > Reported-by: Manjunatha H R <[email-masked]>
> > Signed-off-by: Srikar Dronamraju <[email-masked]>
> 
> Applied to powerpc next, thanks.
> 
> https://git.kernel.org/powerpc/c/2ea62630681027c455117aa471ea3a
> 

Once it gets to Linus's tree, can we request this to be included in
stable trees?

-- 
Thanks and Regards
Srikar Dronamraju