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SubjectRe: apache threads not balanced over all CPU cores, schedular problem or apache?
On 22:48 Thu 13 Nov     , Andy Lutomirski wrote:
> kyle wrote:

> >top - 12:44:42 up 8 days, 15:45, 7 users, load average: 2.07, 1.86, 2.02
> >Tasks: 251 total, 1 running, 249 sleeping, 0 stopped, 1 zombie
> >Cpu0 : 0.5%us, 0.5%sy, 0.0%ni, 99.0%id, 0.0%wa, 0.0%hi, 0.0%si,
> >0.0%st
> >Cpu1 : 14.6%us, 4.4%sy, 0.0%ni, 62.6%id, 17.0%wa, 0.0%hi, 1.5%si,
> >0.0%st
> >Cpu2 : 4.3%us, 1.4%sy, 0.0%ni, 93.8%id, 0.0%wa, 0.5%hi, 0.0%si,
> >0.0%st
> >Cpu3 : 0.0%us, 0.0%sy, 0.0%ni, 98.0%id, 2.0%wa, 0.0%hi, 0.0%si,
> >0.0%st
> >Mem: 8117172k total, 8060936k used, 56236k free, 357488k buffers
> >Swap: 208824k total, 8436k used, 200388k free, 5765168k cached
>
> Looks like you're mostly idle or waiting for I/O. From this
> information, it looks like the kernel is probably doing the right thing:
> keeping a lot of processes that share the same memory and run for very
> short periods of time on the same cores to minimize cacheline bouncing.
>
> >
> >All httpd are running on cpu1 and cpu2 only for several hours, after that,
> >all httpd may run on cpu1 and cpu3, or cpu2 and cpu3, etc. again for
> >several
> >hours.
> >
> >Since the apache is in prefork mode, every httpd instance should be quite
> >independant, I suppose the CPU schedular should balance the processes over
> >the avaiable cores. However never seen httpd processes evenly distributed
> >to
> >3 cores, or 4 cores.
>
> Is there any reason to expect it to run faster if it were balanced evenly?

Totally convincing. Thanks Andy for making this clear. I/O-bound processes
reap no advantage from processor-level parallelism.

-
Rahul





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