Messages in this thread | | | Date | Thu, 13 Nov 2008 22:48:25 -0500 | From | Andy Lutomirski <> | Subject | Re: apache threads not balanced over all CPU cores, schedular problem or apache? |
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kyle wrote: > Hi, > > Please cc me if possible. > > I have a machine with Intel Q9300 4-core CPU, 8GB RAM. It runs apache 2.0.63 > with traditional prefork MPM. > It's a high traffic site, most of the time there's over 100 httpd processes > running and at peak hours around 200. > > I found that most of the time, all httpd processes are running at 2 CPU > cores only, sometime it's cpu0 and cpu1, sometime it's cpu1 and cpu3, > sometime it's cpu0 and cpu2 ... etc. It may take several hours the processes > "migrate" from 2 cores to another 2. To make it clear: > > 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?
--Andy
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