[Ksummit-discuss] [TOPIC] Application performance: regressions, controlling preemption

[Josh Triplett]

On Mon, May 12, 2014 at 10:32:27AM -0400, Chris Mason wrote:
> Hi everyone,
> 
> We're in the middle of upgrading the tiers here from older kernels (2.6.38,
> 3.2) into 3.10 and higher.
> 
> I've been doing this upgrade game for a number of years now, with different
> business cards taped to my forehead and with different target workloads.
> 
> The result is always the same...if I'm really lucky the system isn't slower,
> but usually I'm left with a steaming pile of 10-30% regressions.

How automated are your benchmark workloads, how long do they take, and
how consistent are they from run to run (on a system running nothing
else)?  What about getting them into Fengguang Wu's automated patch
checker, or a similar system that checks every patch or pull rather than
just full releases?  If we had feedback at the time of patch submission
that a specific patch made the kernel x% slower for a specific
well-defined workload, that would prove much easier to act on than just
a comparison of 3.x and 3.y.

- Josh Triplett