linux-kernel - Re: Scheduler patches: 6x performance increase when system is under heavy load

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Date:   Tue, 20 Dec 2016 14:59:29 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexandre-Xavier Labonté-Lamoureux 
        <axdoomer@...il.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: Scheduler patches: 6x performance increase when system is under
 heavy load


Sorry for the delay, got side-tracked for a bit..

On Wed, Dec 14, 2016 at 12:15:25AM -0500, Alexandre-Xavier Labonté-Lamoureux wrote:
> > Which of the 4 patches does this?
> 
> I used all the 4 patches at the same time. Each patch fixes a
> different bug. Would you like me to try each of them individually?

Yes.

> Were you already aware of each of these bugs?

I had seen the paper and the patches. One of the issues has been fixed,
one is a non-issue and we had ideas about at least one other and I
cannot quite remember what the 4th was.

> > Also, what hypervisor are you using and what does the output of booting
> > with "sched_debug" look like?
> 
> I was running the distro in VirualBox on Fedora. Here's the info from
> /proc/sched_debug:
> https://justpaste.it/11dhb
> dmesg: https://justpaste.it/11dhr
> 

Ah, I meant dmesg with the "sched_debug" boot cmdline option (and
probably: "debug ignore_loglevel" added too) of the unmodified kernel.

> > Lastly, can you reproduce on real hardware?
> 
> No. On real hardware, I tested in Ubuntu on an i7-4790 3.60GHz CPU
> without disabling HT and I saw no difference between CFS, the patched
> kernel and MuQSS. If I get to know a reason why one would be better
> than the other, I'd take the time to test it on more hardware. I'm
> curious how I got such a performance improvement in my VM.

OK, I'll also have to look at VirtualBox sources to see if they use
paravirt locking bits, not having support for that could make a
significant difference I suppose.