Andriy Gapon wrote:
On 04/04/2018 03:52, Peter wrote:
Lets run an I/O-active task, e.g, postgres VACUUM that would
continuousely read from big files (while doing compute as well [1]):
Not everyone has a postgres server and a suitable database.
Could you please devise a test scenario that demonstrates the problem and that
anyone could run?
Andriy,
and maybe nobody anymore has such old system that is CPU-bound instead
of IO-bound. I'd rather think about reproducing it on my IvyBridge.
I know for sure that it is *not* specifically dependent on postgres.
What I posted was the case when an endless-loop piglet starves a
postgres VACUUM - and there we see a very pronounced effect of almost
factor 100.
When I first clearly discovered it (after a long time of belly-feeling
that something behaves strange), it was postgres pg_dump (which does
compression, i.e. CPU-bound) as the piglet starving an bacula-fd
backup that would scan the filesystem.
So, there is a general rule: we have one process that is a CPU-hog, and
another process that does periodic I/O (but also *some* compute). and
-important!- nothing else.
If we understand the logic of the scheduler, that information should
already suit for some logical verification *eg* - but I will see if I
get it reprocuved on the IvyBridge machine and/or see if I get a
testcase together. May take a while.
P.
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