Re: [x86-tip] strange nr_cpus= boot regression

From: Thomas Gleixner
Date: Mon Sep 26 2016 - 13:39:30 EST

CC'ed: Dou Liyang

On Mon, 26 Sep 2016, Mike Galbraith wrote:

> I've encountered a strange regression in tip, symptom is that if you
> boot with nr_cpus=nr_you_have, what actually boots is nr_you_have/2.
> Do not pass nr_cpus=, and all is well.

What's the number of possible cpus in your system?

> Bisection repeatedly goes as below, pointing to the nodeid merge,
> despite both timers/core and x86/apic (nodeid) being fine. Take tip
> HEAD, extract all of the commits from nodeid (plus the fix), and revert
> them in a quilt tree, the tree remains busted.

So you remove all the nodeid commits from tip/master and it's still broken?

> Checkout the timers/core merge commit, and merge nodeid with that, it is
> indeed bad.

> Bisecting takes you right the merge commit, with no commit
> being 'bad', see logs.

That's more than strange. An empty merge commit being the culprit.