CONFIG_NO_HZ causing poor console responsiveness

[Timur Tabi]

On Tue, Jun 29, 2010 at 2:54 PM, Timur Tabi <timur at freescale.com> wrote:
> I'm adding support for a new e500-based board (the P1022DS), and in
> the process I've discovered that enabling CONFIG_NO_HZ (Tickless
> System / Dynamic Ticks) causes significant responsiveness problems on
> the serial console.  When I type on the console, I see delays of up to
> a half-second for almost every character.  It acts as if there's a
> background process eating all the CPU.

I finally finished my git-bisect, and it wasn't that helpful.  I had
to skip several commits because the kernel just wouldn't boot:

There are only 'skip'ped commits left to test.
The first bad commit could be any of:
6bc6cf2b61336ed0c55a615eb4c0c8ed5daf3f08
8b911acdf08477c059d1c36c21113ab1696c612b
21406928afe43f1db6acab4931bb8c886f4d04ce
5ca9880c6f4ba4c84b517bc2fed5366adf63d191
a64692a3afd85fe048551ab89142fd5ca99a0dbd
f2e74eeac03ffb779d64b66a643c5e598145a28b
c6ee36c423c3ed1fb86bb3eabba9fc256a300d16
e12f31d3e5d36328c7fbd0fce40a95e70b59152c
13814d42e45dfbe845a0bbe5184565d9236896ae
b42e0c41a422a212ddea0666d5a3a0e3c35206db
39c0cbe2150cbd848a25ba6cdb271d1ad46818ad
beac4c7e4a1cc6d57801f690e5e82fa2c9c245c8
41acab8851a0408c1d5ad6c21a07456f88b54d40
6427462bfa50f50dc6c088c07037264fcc73eca1
c9494727cf293ae2ec66af57547a3e79c724fec2
We cannot bisect more!

These correspond to a batch of scheduler patches, most from Mike Galbraith.

I don't know what to do now.  I can't test any of these commits.  Even
if I could, they look like they're all part of one set, so I doubt I
could narrow it down to one commit anyway.

-- 
Timur Tabi
Linux kernel developer at Freescale