* Sergey Koposov (kopo...@ast.cam.ac.uk) wrote: > I did a specific test with just 6 threads (== number of cores per cpu) > and ran it on a single phys cpu, it took ~ 12 seconds for each thread, > and when I tried to spread it across 4 cpus it took 7-9 seconds per > thread. But all these numbers are anyway significantly better then > when I didn't use taskset. Which probably means without it the > processes were jumping from core to core ? ...
Oh, and wrt why 'cat' isn't really affected by this issue- that's because 'cat' isn't *doing* anything, CPU wise, really. The PG backends are actually doing real work and therefore they have both CPU state and memory accesses which are impacted when the process is moved from one core to another. If this system has NUMA (where memory is associated with a set of cores), then that can make it more painful when threads are being moved between cores also, because suddenly the memory you were accessing (which was 'fast') is now taking longer because you're having to go through another CPU to get to it. Thanks, Stephen
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