Bugzilla Bug 115781

Executing simple CPU test on Intel(R) Pentium(R) 4 CPU 3.00GHz (with Hyper 
Threading enabled) show about 3 times slowdown when 2 processes use CPU 
simultaneously. This slowdown exists in:
- sys-kernel/hardened-sources-2.6.14-r1
- sys-kernel/gentoo-sources-2.6.14-r4
- sys-kernel/vanilla-sources-2.6.14.2
but there no such slowdown in kernel supplied with Fedora Core 2 "Linux version 
2.6.14-051115a (somebody@somewhere) (gcc version 3.3.5 (Debian 1:3.3.5-13)) #1 
SMP Tue Nov 15 13:06:41 CET 2005" (probably this kernel isn't really from 
Fedora, maybe it was compiled by my ISP for my dedicated server, don't sure).

My CPU test is simple. Here results from Fedora:

---cut---
# time perl -e '$pid=fork if @ARGV; print "$$ started\n"; $i++ for 1..100000000; 
print "$$ finished\n"; print("waiting for $pid\n"), wait() if $pid'
1001 started
1001 finished

real    0m11.118s
user    0m11.117s
sys     0m0.000s

# time perl -e '$pid=fork if @ARGV; print "$$ started\n"; $i++ for 1..100000000; 
print "$$ finished\n"; print("waiting for $pid\n"), wait() if $pid' 1
1003 started
1002 started
1003 finished
1002 finished
waiting for 1003

real    0m23.818s          ### ATTENTION HERE !!!
user    0m47.627s
sys     0m0.000s
---cut---

and here results from Gentoo (with any *-sources listed above):

---cut---
# time perl -e '$pid=fork if @ARGV; print "$$ started\n"; $i++ for 1..100000000; 
print "$$ finished\n"; print("waiting for $pid\n"), wait() if $pid'
4493 started
4493 finished

real    0m12.490s
user    0m12.485s
sys     0m0.004s

# time perl -e '$pid=fork if @ARGV; print "$$ started\n"; $i++ for 1..100000000; 
print "$$ finished\n"; print("waiting for $pid\n"), wait() if $pid' 1
4495 started
4494 started
4494 finished
waiting for 4495
4495 finished

real    1m7.266s          ### ATTENTION HERE !!!
user    2m14.432s
sys     0m0.000s
---cut---

All these kernels was compiled with exactly same .config (which I take from 
Fedora's /proc/config.gz). All these kernels show nearly same information in /
proc/cpuinfo, dmesg and lsmod.

Probably some patch (from Fedora?) should be added to gentoo-sources & hardened-
sources to fix this issue...

*gentoo-sources-2.6.14-r5 (15 Dec 2005)

  15 Dec 2005; Daniel Drake <dsd@gentoo.org>
  +gentoo-sources-2.6.14-r5.ebuild:
  Update to Linux 2.6.14.4. Really fix the hyperthreading slowdown. Fix NUMA
  boot problem.

Reopen it if still does not work when with latest gentoo-sources.

No, it doesn't work with sys-kernel/gentoo-sources-2.6.14-r5. :-(

Don't sure is it important, but I use sys-devel/gcc-3.4.4-r1 (HARDENED) for 
compiling kernel. And, just for the case, here is my `emerge info`:

---cut---
Portage 2.0.51.22-r3 (hardened/x86/2.6, gcc-3.4.4, glibc-2.3.5-r2, 2.6.14-
gentoo-r5 i686)
=================================================================
System uname: 2.6.14-gentoo-r5 i686 Intel(R) Pentium(R) 4 CPU 3.00GHz
Gentoo Base System version 1.6.13
dev-lang/python:     2.3.5-r2, 2.4.2
sys-apps/sandbox:    1.2.12
sys-devel/autoconf:  2.13, 2.59-r6
sys-devel/automake:  1.4_p6, 1.5, 1.6.3, 1.7.9-r1, 1.8.5-r3, 1.9.6-r1
sys-devel/binutils:  2.16.1
sys-devel/libtool:   1.4.3-r4, 1.5.20
virtual/os-headers:  2.6.11-r2
ACCEPT_KEYWORDS="x86"
AUTOCLEAN="yes"
CBUILD="i686-pc-linux-gnu"
CFLAGS="-O2 -march=pentium4 -pipe"
CHOST="i686-pc-linux-gnu"
CONFIG_PROTECT="/etc /usr/kde/2/share/config /usr/kde/3/share/config /usr/share/
config /var/qmail/alias /var/qmail/control"
CONFIG_PROTECT_MASK="/etc/gconf /etc/terminfo /etc/env.d"
CXXFLAGS="-O2 -march=pentium4 -pipe"
DISTDIR="/usr/portage-distfiles"
FEATURES="autoconfig buildpkg ccache distlocks sandbox sfperms strict userpriv 
usersandbox"
GENTOO_MIRRORS="http://pandemonium.tiscali.de/pub/gentoo/ ftp://pandemonium.
tiscali.de/pub/gentoo/ http://ftp-stud.fht-esslingen.de/pub/Mirrors/gentoo/ 
http://ftp.belnet.be/mirror/rsync.gentoo.org/gentoo/"
MAKEOPTS="-j3"
PKGDIR="/usr/portage-packages"
PORTAGE_TMPDIR="/var/tmp"
PORTDIR="/usr/portage"
PORTDIR_OVERLAY="/usr/local/portage /usr/local/portage-java-experimental /usr/
local/portage-power"
SYNC="rsync://rsync.gentoo.org/gentoo-portage"
USE="acpi aim apache2 berkdb bzip2 crypt curl dlloader expat gd gdbm gif 
hardened icq idn imagemagick imap irc jabber java javascript jpeg junit 
lm_sensors mailbox mbox mmx msn mysql ncurses nls nptl nptlonly pam pcre perl 
pic png pwdb python readline rss slang sse sse2 ssl sysfs tcpd tiff truetype 
udev userlocales x86 xinetd xml2 yahoo zlib userland_GNU kernel_linux 
elibc_glibc"
Unset:  ASFLAGS, CTARGET, LANG, LC_ALL, LDFLAGS, LINGUAS
---cut---

Please test vanilla-sources-2.6.15_rc6 with this additional patch applied:
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff_plain;h=1e483969930a82e16767884449f3a121a817ef00;hp=4c0335526c95d90a1d958e0059f40a5745fc7c5d

(In reply to comment #3)
> Please test vanilla-sources-2.6.15_rc6 with this additional patch applied:
> http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff_plain;h=1e483969930a82e16767884449f3a121a817ef00;hp=4c0335526c95d90a1d958e0059f40a5745fc7c5d

Bad idea. :-(
With this patch kernel don't boot. This is dedicated server on good enough
hosting which provide 'serial console' and 'rescue network boot'. I've checked
serial console, but there was no output from booting kernel, so it's probably
hang before serial console driver was loaded. Then I've used 'rescue network
boot' mode to login to my server and change grub.conf to load another kernel -
same vanilla-sources-2.6.15_rc6, but without that patch. It's boot ok, but
"hyper threading slowdown" bug still exists in this version.

I notice some part of this patch in '#ifdef CONFIG_HOTPLUG_CPU', so I've
enabled in my kernel CONFIG_HOTPLUG_CPU and tried again to boot kernel with
this patch - without success - it hangs again.

Have you tried 2.6.15-rc6 without the patch?

Also, maybe you could try 2.6.14-r5 with CONFIG_HOTPLUG_CPU enabled and see if
that helps.

Yeah, I have tried 2.6.15-rc6 without the patch (see comment #4).

I've just tried 2.6.14-r5 with CONFIG_HOTPLUG_CPU enabled. This don't fix the
bug.

Looks like an upstream bug - if you still get this with 2.6.15 vanilla please
post to the LKML and reference this bug.

Thanks!

2.6.15 vanilla hangs if CONFIG_HOTPLUG_CPU enabled. If CONFIG_HOTPLUG_CPU
disabled - it boot ok, but 'hyper threading slowdown' issue still exists. :-(
Enabling/disabling CONFIG_SCHED_SMT has no effect.