[DragonFlyBSD - Bug #884] Performance/memory problems under filesystem IO load

[bugtracker-admin at leaf.dragonflybsd.org]

Issue #884 has been updated by alexh.


On 2014-02-18 14:47, bugtracker-admin at leaf.dragonflybsd.org wrote:
> I don't see the high usage corecode showed in his test.
> 
> Matt, there was a ton of work in the VM subsystem, is it possible that
> this is not the case anymore?

Well, we most definitely have quite bad problems under heavy I/O load. 
Interactive performance drops significantly. Getting BFQ or similar 
dsched policy up to scratch would go a long way here.

Cheers,
Alex

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Bug #884: Performance/memory problems under filesystem IO load
http://bugs.dragonflybsd.org/issues/884#change-11765

* Author: hasso
* Status: In Progress
* Priority: High
* Assignee: 
* Category: VM subsystem
* Target version: 3.8.0
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During testing drive with dd I noticed that there are serious performance 
problems. Programs which need disk access, block for 10 and more seconds. 
Sometimes they don't continue the work until dd is finished. Raw disk access 
(ie not writing to file, but directly to the disk) is reported to be OK (I 
can't test it myself).

All tests are done with this command:
dd if=/dev/zero of=./file bs=4096k count=1000

Syncing after each dd helps to reproduce it more reliably (cache?).

There is one more strange thing in running these tests. I looked at memory 
stats in top before and after running dd.

Before:
Mem: 42M Active, 40M Inact, 95M Wired, 304K Cache, 53M Buf, 795M Free
After:
Mem: 70M Active, 679M Inact, 175M Wired, 47M Cache, 109M Buf, 1752K Free

And as a side effect - I can't get my network interfaces up any more after 
running dd - "em0: Could not setup receive strucutres".



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