On Wed, 20 Nov 2013, Tim Connors wrote:
Hi all,
On your most overloaded (cpu/fork rate/context switches - ignoring memory network, disk and swap etc), what is the maximum number of context switches per second per core (ie divide sar -w output by 16 if you have a 16 core box) you measure?
Does anyone know what the maximum number of context switches per core you can expect on xeon level hardware?
I'm trying to claim we get overloaded when we reach a little less than 10,000 cswch/s per second, but we've lost all the historical data.
Indeed, is there going to be a maximum for a given piece of hardware (eg, maximum amount of interrupts that can be generated per second; time spent in the interrupt handler that all has to be handled by only one CPU hence explaining why CPU system usage never looks alarming (divide by 8 on some servers, by 16 on others); big kernel lock somewhere in the context switch code)? When we have these overloads, nothing else we measure seems to be approaching any limit. The servers have plenty of CPU left, and there's no real difficulty logging into them. Anything else I should be looking at? Fork rate is tiny (1 or 2 per second). Network bandwidth is fine. Not sure that I've noticed network packet limitations (4k packets per second per host when it failed last time, generating 16000 interrupts/second total per host). -- Tim Connors