Subject: recent amd64 slowless caused by x86pmap merge
To: None <>
From: matthew green <>
List: tech-kern
Date: 10/29/2007 13:46:52
hi folks.

i've been benchmarking builds on a (dual) athlon64 x2 running
amd64 mode.   i recently noticed that my builds were slower
and i have tracked down the slowness to the x86pmap merge.  a
bit of binary searching led me to believe it was that, and 
backing out the change on -current gives me similar performance
to the previous kernel.

it's a fairly severe degradation - i see almost 10% more runtime
to build a kernel!

here are some numbers to illustrate:

plain -current:

	256.8u 92.5s 2:56.98 197.4% 0+0k 0+7755io 0pf+0w
	256.0u 93.6s 2:56.94 197.6% 0+0k 0+7751io 0pf+0w

old amd64/pmap.c with -current:

	241.7u 77.5s 2:41.72 197.4% 0+0k 0+7742io 0pf+0w
	242.7u 76.4s 2:41.71 197.4% 0+0k 0+7747io 0pf+0w

1 month old kernel:

	241.3u 73.2s 2:41.65 194.5% 0+0k 33+7748io 125pf+0w
	242.1u 72.6s 2:39.51 197.3% 0+0k 0+7745io 0pf+0w

(so there may infact be more slowness since a month ago, but
i have not looked into that at all -- just noticed it now.)

so that is adding over 15 seconds to a 160 second build..