Message-ID: <3F376597.9000708@cyberone.com.au>
Date: Mon, 11 Aug 2003 19:44:55 +1000
From: Nick Piggin <piggin@cyberone.com.au>
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To: Con Kolivas <kernel@kolivas.org>
CC: Martin Schlemmer <azarah@gentoo.org>,
       linux kernel mailing list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH]O14int
References: <200308090149.25688.kernel@kolivas.org> <200308111608.18241.kernel@kolivas.org> <3F375EBD.5030106@cyberone.com.au> <200308111943.49235.kernel@kolivas.org>
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Con Kolivas wrote:

>On Mon, 11 Aug 2003 19:15, Nick Piggin wrote:
>
>>Con Kolivas wrote:
>>
>>>On Mon, 11 Aug 2003 15:44, Martin Schlemmer wrote:
>>>
>>>>On Sat, 2003-08-09 at 11:04, Con Kolivas wrote:
>>>>
>>>>>On Sat, 9 Aug 2003 01:49, Con Kolivas wrote:
>>>>>
>>>>>>More duck tape interactivity tweaks
>>>>>>
>>>>>s/duck/duct
>>>>>
>>>>>
>>>>>>Wli pointed out an error in the nanosecond to jiffy conversion which
>>>>>>may have been causing too easy to migrate tasks on smp (? performance
>>>>>>change).
>>>>>>
>>>>>Looks like I broke SMP build with this. Will fix soon; don't bother
>>>>>trying this on SMP yet.
>>>>>
>>>>Not to be nasty or such, but all these patches have taken
>>>>a very responsive HT box to one that have issues with multiple
>>>>make -j10's running and random jerkyness.
>>>>
>>>A UP HT box you mean? That shouldn't be capable of running multiple make
>>>-j10s without some noticable effect. Apart from looking impressive, there
>>>is no point in having 30 cpu heavy things running with only 1 and a bit
>>>processor and the machine being smooth as silk; the cpu heavy things will
>>>just be unfairly starved in the interest of appearance (I can do that
>>>easily enough). Please give details if there is a specific issue you
>>>think I've broken or else I wont know about it.
>>>
>>Yeah make -j10s won't be without impact, but I think for a lot of
>>interactive stuff they don't need a lot of CPU, just to get it
>>in a timely manner. And Martin did say it had been responsive.
>>Sounds like in this case your changes are causing the interactive
>>stuff to get less CPU or higher scheduling latency?
>>
>
>Sigh..,
>
>No, it sounds to me like things are expiring faster than on default. He didn't 
>say make -j10, it was multiple -j10s. This is one where you simply cannot let 
>the scheduler keep starving the make -j10s indefinitely for X; on a server or 
>multiuser box X will simply cause unfair starvation. I'm trying to find a 
>workaround for this without rewriting whole sections of the scheduler code, 
>but I'm just not sure I should be trying to optimise for a desktop that runs 
>loads >16 per cpu. (I'll keep trying though, but if there is no workaround 
>that remains fair it wont happen)
>
>

Yep, I did see the multiple j10s ;)
I wasn't aware that there was longer term starvation of gccs by X. I
thought the scheduler had always been quite good at evening up the
total CPU time used and a change you made had recently introduced a
latency or interactiveness problem.

But Martin didn't give a very detailed description of the problem,
and no I definitely don't think you should be aiming at fixing
his problem if it causes starvation or harms more common loads.


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