Subject: recent amd64 slowless caused by x86pmap merge
To: None <email@example.com>
From: matthew green <firstname.lastname@example.org>
Date: 10/29/2007 13:46:52
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:
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..