Large spikes in latencies
zarniwhoop at ntlworld.com
Fri May 29 16:04:05 PDT 2015
On Fri, May 29, 2015 at 06:14:46PM -0400, Yogi A. Patel wrote:
> > On 05/28/2015 08:54 PM, Michel Dänzer wrote:
> > Can you narrow down when the problem was introduced in the kernel,
> > ideally with git bisect?
> I did a few experiments and here is an update:
> + It seems that whatever is causing this is from drm/radeon and it came in sometime between 3.8.13 and 3.10.32. The dmesg output from 3.10.32 is attached, too
> + the latencies are worse on 3.14 (40us) than on 3.10 (20-30us) regardless of the card.
> + latencies on 3.8 for both cards are below 10us.
Just in case you don't realise how stable kernel releases happen:
First, Linus release .0. For most people, these kernels work ok
most of the time. Then gradual fixes appear during the development
of a later kernel, and get applied by the stable team. So, I
suggest that an approach something like this might help:
Begin by testing 3.10.0 and (ideally) 3.8.0.
Is 3.10.0 worse than 3.8 ? If it is, the problem was introduced
between 3.8 (good) and 3.10 (bad) and you can bisect linus's tree.
If 3.10.0 was good, the problem appeared in the 3.10 _stable_ tree.
For something like that, I have on occasion been tempted to take a
broad-brush initial approach and try the released versions - in this
case I might begin by trying e.g. 3.10.16, 3.10.8 or 3.10.24, etc to
get a better feeling for when it went bad. But ultimately,
bisecting the 3.10 stable tree will be the way to go.
Also, it sounds as if 3.14 is a different, or extra, problem.
Would it be practical for you to move to a newer version if that
solved the problem ? If so, you could try 4.0.latest just in case
it is already fixed. A couple of times, I've had to do bisection in
-rc kernels, only to discover that a commit during the current week
had already removed the problem I had.
Nanny Ogg usually went to bed early. After all, she was an old lady.
Sometimes she went to bed as early as 6 a.m.
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