Re: [PATCH 00/26] Performance-related backports for 4.12.2

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On Tue, Jul 25, 2017 at 09:14:35AM +0100, Mel Gorman wrote:
> On Mon, Jul 24, 2017 at 04:29:05PM -0700, Greg KH wrote:
> > On Mon, Jul 24, 2017 at 05:44:01PM +0100, Mel Gorman wrote:
> > > On Thu, Jul 20, 2017 at 10:21:18PM +0100, Mel Gorman wrote:
> > > > This is a second round of performance-related backports based on low-hanging
> > > > fruit in the 4.13 merge window based on 4.12.2.
> > > > 
> > > > As before, these have only been tested on 4.12-stable.  While they may
> > > > merge against older kernels, I have no data on how it behaves and cannot
> > > > guarantee it's a good idea so I don't recommend it.  There will also be
> > > > some major conflicts that are not trivial to resolve.
> > > > 
> > > > For most of the tests I conducted, the impact is marginal but patches the
> > > > first two sets of patches are important for large machines and for uses
> > > > of nohz_full. The load balancing patch is fairly specific but measurable.
> > > > The removal of unnecessary IRQ disabling/enabling is borderline in terms of
> > > > performance but they are trivial patches and avoiding unnecessary expensive
> > > > operations is always a plus.
> > > > 
> > > 
> > > With 4.12.3, the patches 1-17 can be dropped.
> > 
> > Really?  Why, what happened in .3 that make the need for those 17
> > patches just "go away"?
> > 
> 
> One of the biggest motivation of the series was to bring in these
> commits that are now in -stable
> 
> d5ba2df79bc6ae02927d5465e93eb635809e6db5 sched/topology: Fix overlapping sched_group_mask
> 3397c1f0371a49f52635c9e60e552ef3c91fa10f sched/topology: Optimize build_group_mask()
> e64918b4b7c3bac472198d7b59b6092a78092169 sched/topology: Fix building of overlapping sched-groups
> 
> The series now needs to be rebased on top to deal with minor collisions
> but once it is, there is only one notable fix left related to scheduler
> topology -- "sched/topology: Fix overlapping sched_group_capacity" and it
> is borderline. The bulk of the rest are cleanups, micro-optimisations,
> simplifications and then documentation so the whole thing is
> understandable. The rebase is trivial (collisions with comments) but we
> can also live without them.
> 
> > > The main commit left over
> > > that is missing from this series was "sched/topology: Fix overlapping
> > > sched_group_capacity" which is relatively minor in impact. The rest were
> > > to bring the schedulers more or less in line so debugging problems in
> > > 4.12-stable would be easier to compare with mainline and to make the 4.12
> > > scheduler easier to understand.
> > > 
> > > The rest of the series should apply ok on top of 4.12.3 if you'd like to
> > > pick it up.
> > 
> > So just patches 18-26?
> > 
> 
> Yes, that will then be the accounting fixes for nohz_full users, a load
> balancer fix when some processes are pinned to CPUs and a few minor
> optimisations that avoid unnecessary disabling of IRQs.

Ok, I've queued patches 18-26 up now, thanks!

greg k-h



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