Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]

Gene Heskett
2007-04-15T16:59:05Z

On Sunday 15 April 2007, Con Kolivas wrote:
>On Monday 16 April 2007 01:16, Gene Heskett wrote:
>> On Sunday 15 April 2007, Pekka Enberg wrote:
>> >On 4/15/07, hui Bill Huey <billh@gnuppy.monkey.org> wrote:
>> >> The perception here is that there is that there is this expectation
>> >> that sections of the Linux kernel are intentionally "churn squated" to
>> >> prevent any other ideas from creeping in other than of the owner of
>> >> that subsytem
>> >
>> >Strangely enough, my perception is that Ingo is simply trying to
>> >address the issues Mike's testing discovered in RDSL and SD. It's not
>> >surprising Ingo made it a separate patch set as Con has repeatedly
>> >stated that the "problems" are in fact by design and won't be fixed.
>>
>> I won't get into the middle of this just yet, not having decided which dog
>> I should bet on yet. I've been running 2.6.21-rc6 + Con's 0.40 patch for
>> about 24 hours, its been generally usable, but gzip still causes lots of 5
>> to 10+ second lags when its running. I'm coming to the conclusion that
>> gzip simply doesn't play well with others...
>
>Actually Gene I think you're being bitten here by something I/O bound since
>the cpu usage never tops out. If that's the case and gzip is dumping
>truckloads of writes then you're suffering something that irks me even more
>than the scheduler in linux, and that's how much writes hurt just about
>everything else. Try your testcase with bzip2 instead (since that won't be
>i/o bound), or drop your dirty ratio to as low as possible which helps a
>little bit (5% is the minimum)
>
>echo 5 > /proc/sys/vm/dirty_ratio
>
>and finally try the braindead noop i/o scheduler as well.
>
>echo noop > /sys/block/sda/queue/scheduler
>
>(replace sda with your drive obviously).
>
>I'd wager a big one that's what causes your gzip pain. If it wasn't for the
>fact that I've decided to all but give up ever trying to provide code for
>mainline again, trying my best to make writes hurt less on linux would be my
>next big thing [tm].

Chuckle, possibly but then I'm not anything even remotely close to an expert
here Con, just reporting what I get. And I just rebooted to 2.6.21-rc6 +
sched-mike-5.patch for grins and giggles, or frowns and profanity as the case
may call for.

>Oh and for the others watching, (points to vm hackers) I found a bug when
>playing with the dirty ratio code. If you modify it to allow it drop below
> 5% but still above the minimum in the vm code, stalls happen somewhere in
> the vm where nothing much happens for sometimes 20 or 30 seconds worst case
> scenario. I had to drop a patch in 2.6.19 that allowed the dirty ratio to
> be set ultra low because these stalls were gross.

I think I'd need a bit of tutoring on how to do that. I recall that one other
time, several weeks back, I thought I would try one of those famous echo this
>/proc/that ideas that went by on this list, but even though I was root,
apparently /proc was read-only AFAIWC.

>> Amazing to me, the cpu its using stays generally below 80%, and often
>> below 60%, even while the kmail composer has a full sentence in its buffer
>> that it still hasn't shown me when I switch to the htop screen to check,
>> and back to the kmail screen to see if its updated yet. The screen switch
>> doesn't seem to lag so I don't think renicing x would be helpfull. Those
>> are the obvious lags, and I'll build & reboot to the CFS patch at some
>> point this morning (whats left of it that is :). And report in due time
>> of course

And now I wonder if I applied the right patch. This one feels good ATM, but I
don't think its the CFS thingy. No, I'm sure of it now, none of the patches
I've saved say a thing about CFS. Backtrack up the list time I guess, ignore
me for the nonce.

--
Cheers, Gene
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Microsoft: Re-inventing square wheels

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