Re: Testing memory performance

[Sad Clouds <cryintothebluesky%gmail.com@localhost>]

On Mon, 19 Nov 2018 01:06:45 -0000 (UTC)
mlelstv%serpens.de@localhost (Michael van Elst) wrote:

> munlock fails when not the whole range has been locked, Since the
> range is rounded to page boundaries, there could be some overlap.
> 
Are you referring to virtual or physical range of addresses? As far as
I remember all memory ranges were power of 2 and much greater than 
4 KiB. Maybe memory alignment has to be on page boundary, I'll see if
it helps changing malloc to posix_memalign.

> Another effect on your system is NUMA. Linux will allocate memory
> on the CPU that requests it when possible. NetBSD has no idea about
> NUMA. On your system that can easily have a 20-30% impact on memcpy
> speed.
> 
> If a thread sleeps, it either is doing a system call, or the scheduler
> doesn't allocate a CPU for it. The latter shouldn't happen in netbsd-8
> for CPU bound user threads.
> 
> But without seeing your code, it's difficult to tell what happens.

Speed difference is about 2.5 times, so way bigger than 30% you
mentioned. Also, there is a simple loop that calls memcpy, no syscalls
of any kind, but for some reason threads are idle 60% of the time. I'll
run some more tests and provide more details.