On Sun, 22 Feb 2009, Maxim Sobolev wrote:
Hi Jeff,
I have a single-CPU system with P4 HTT-enabled processor (7.1-RELEASE-p3),
kernel compiled with SCHED_ULE.
This is because machdep.hlt_logical_cpus doesn't do what you think it does.
It causes HTT cores to invoke the hlt instruction in their idle loop, causing
them to sleep until they receive an interrupt. For 4BSD, which uses a "pull"
model (on the whole) to bring work from work queues, this means that CPUs will
go to sleep and remain that way unless they're actively receiving interrupts.
For ULE, which uses "push" as well as "pull", threads will constantly be being
shed from too-busy CPUs to apparently idle ones under load. The only reliable
way to disable hyperthreading is to do so using your BIOS setting, or use
loader.conf to disable probing of the pics on unwanted cores, which will cause
the CPUs not to be enumerated and hence not used. We don't support taking
CPUs fully offline with any scheduler, although you can use the cpuset
facility to prevent threads from running on specific cores. You could imagine
teaching ULE (and presumably 4BSD) about policies such as "Don't use HTT
cores", or perhaps just cpuset about those policies.
Robert N M Watson
Computer Laboratory
University of Cambridge
Copyright (c) 1992-2009 The FreeBSD Project.
Copyright (c) 1979, 1980, 1983, 1986, 1988, 1989, 1991, 1992, 1993, 1994
The Regents of the University of California. All rights reserved.
FreeBSD is a registered trademark of The FreeBSD Foundation.
FreeBSD 7.1-RELEASE-p3 #0: Fri Feb 20 09:53:32 UTC 2009
r...@foo.com:/usr/obj/usr/src/sys/SSP-PRODUCTION7
Timecounter "i8254" frequency 1193182 Hz quality 0
CPU: Intel(R) Pentium(R) 4 CPU 3.00GHz (2992.51-MHz 686-class CPU)
Origin = "GenuineIntel" Id = 0xf34 Stepping = 4
Features=0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE>
Features2=0x441d<SSE3,DTES64,MON,DS_CPL,CNXT-ID,xTPR>
Logical CPUs per core: 2
real memory = 3758030848 (3583 MB)
avail memory = 3674083328 (3503 MB)
ACPI APIC Table: <IntelR AWRDACPI>
FreeBSD/SMP: Multiprocessor System Detected: 2 CPUs
cpu0 (BSP): APIC ID: 0
cpu1 (AP): APIC ID: 1
ioapic0: Changing APIC ID to 2
ioapic0 <Version 2.0> irqs 0-23 on motherboard
ioapic1 <Version 2.0> irqs 24-47 on motherboard
machdep.cpu_idle_hlt: 1
machdep.hlt_cpus: 0
machdep.hlt_logical_cpus: 0
machdep.logical_cpus_mask: 2
If I flip machdep.hyperthreading_allowed sysctl, I still can see processes
scheduled to both logical CPUs, yet, if I check IRQ status in the systat -vm,
the CPU1 is not getting any timer interrupts, while CPU0 gets twice the
normal amount. I wonder if something is broken - I would expect no processes
to be scheduled to the CPU1.
machdep.hyperthreading_allowed=1:
top: http://sobomax.sippysoft.com/~sobomax/ScreenShot458.png
systat -vm: http://sobomax.sippysoft.com/~sobomax/ScreenShot459.png
machdep.hyperthreading_allowed=0:
top: http://sobomax.sippysoft.com/~sobomax/ScreenShot460.png
systat -vm: http://sobomax.sippysoft.com/~sobomax/ScreenShot461.png
Please let me know if any other debug information is needed.
-Maxim
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