On 12/22/2013 05:23 PM, Len Ovens wrote: > > On Sat, 21 Dec 2013, david wrote: > >> Too, late, already have the machine with the i7. I think it only cost >> $15 more than the i5 option. I this particular model's i5 base >> processor has a lower clock rate than the i7 started with. >> >> Just checked the BIOS. No option to turn of hyperthreading. >> > In linux each hyperthread is treated as another core. So if you have 4 > cores, it will look like 8 with hyperthreading on. Every second cpu that > linux sees is a hyperthread. so you only want cpu 0,2,4,and 6. There is > a kernel command line option to have the kernel ignore some cpus, get it > to ignore cpu 1,3,5 and 7. I seem to be off line right now so I can't > look it up. Ah, back up. > isolcpus= cpu_number[, cpu_number,...] > > The blurb for that: > "Remove the specified CPUs, as defined by the cpu_number values, from > the general kernel SMP balancing and scheduler algroithms. The only way > to move a process onto or off an "isolated" CPU is via the CPU affinity > syscalls. cpu_number begins at 0, so the maximum value is 1 less than > the number of CPUs on the system. > > This option is the preferred way to isolate CPUs. The alternative, > manually setting the CPU mask of all tasks in the system, can cause > problems and suboptimal load balancer performance." > > The place to add this to your system (if you don't want enter it every > time you boot) is in GRUBs config. The best place to do this varies with > the ditro. For example, I have found the best place to do this on a > Ubuntu system is in /etc/default/grub.d/ as it does not interfere with > upgrades. > > The place you will see mentioned more often is a file called > /etc/default/grub Look for a line like GRUB_CMDLINE_LINUX="" and edit it > (as root of course) to: > GRUB_CMDLINE_LINUX="isolcpus= 1,3,5,7" > > If you have more than 4 cores(6 or 8), I do not know if cpus higher than > 9 are in hex or dec. > > If you wish to have grub menu options to boot either way.... I would > guess it is time to learn more about GRUB :) It is easy to add menu > items on a static system, but gets much harder on a system with lots of > updates. > > Hmm, there seem to be a lot of irq options too. I wonder if they would > be able to force better irq assignment within the system. I know telling > the bios not to select irqs for USB gives better irq layout for me. > > Anyway, the list of kernel options I based this on is from: > http://oreilly.com/linux/excerpts/9780596100797/kernel-boot-command-line-parameter-reference.html > > > > -- Len Ovens www.ovenwerks.net Hello Len, Thanks for the valuable information! If you don't mind I'll add it to http://wiki.linuxaudio.org/wiki/system%20configuration I thought just disabling them like: CPU=( cpu1 cpu3 cpu5 cpu7 ) for i in "${CPU[@]}" do echo 0 > /sys/devices/system/cpu/$i/online done would do the trick too but on my own system I still can't go lower than -p128 so hopefully the isolcpus parameter improves stability. Best, Jeremy
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