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

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Mon, May 12, 2014 at 04:54:35PM -0700, Josh Triplett wrote:
> 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.

Good point on Fengguang's checker!  I do sometimes get emails from him
noting changes in performance, conveniently bisected down to the commit.

							Thanx, Paul