linux-kernel - Re: x86: 4kstacks default

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Message-ID: <20080420225354.08b1d096@laptopd505.fenrus.org>
Date:	Sun, 20 Apr 2008 22:53:54 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Daniel Hazelton <dhazelton@...er.net>,
	Adrian Bunk <bunk@...nel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Shawn Bohrer <shawn.bohrer@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: x86: 4kstacks default

On Mon, 21 Apr 2008 01:16:22 +0200
Andi Kleen <andi@...stfloor.org> wrote:

> Arjan van de Ven <arjan@...radead.org> writes:
> >
> > it is you who keeps putting up the 50k argument.
> 
> See the links I posted and quote in an earlier message up the thread
> if you don't remember what you wrote yourself.
> 
> I originally only hold up the fragmentation argument (or rather only
> argued against it), until I was corrected by both Ingo and you in the
> earlier thread and you both insisted that 50k threads were the real
> reason'd'etre for 4k stacks.  
> 
> You're saying that was wrong and the fragmentation issue was really
> the real reason for 4k stacks? If both you and Ingo can agree on that
> I would be happy to forget the 50k threads :)

I already corrected you misquoting/misunderstanding me; should I do this again?

> 
> > What I'm talking about is in the 10k to 20k range; and that is
> > actual workloads by real customers.
> 
> On a 32bit kernel? 
> 
> My estimate is that you need around 32k for a functional blocked
> thread in a network server (8k + 2*4k for poll with large fd table
> and wait queues + some pinned dentries and inodes + misc other
> stuff). With 20k you're 625MB into your lowmem which leaves about
> 200MB left on a 3:1 system with 16GB (and ~128MB mem_map).  That
> might work for some time, but I expect it will fall over at some
> point because there is just too much pinned lowmem and not enough
> left for other stuff (like networking buffers etc.) 
> 
> 10k sounds more doable. But again do 4k more or less make 
> a big difference with the other thread overhead? I don't think so.

no but the other ones are order 0..

-- 
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