Subject: Re: The disappearing sys_call_table export.
From: Terje Eggestad <terje.eggestad@scali.com>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>,
       Arjan van de Ven <arjanv@redhat.com>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       D.A.Fedorov@inp.nsk.su
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Date: 05 May 2003 15:23:39 +0200
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On Mon, 2003-05-05 at 13:16, Alan Cox wrote:
> On Llu, 2003-05-05 at 10:33, Terje Eggestad wrote:
> > 1. performance is everything. 
> 
> Then you can live with building custom patched kernels
> 

If there was numerous issues, sure. But every time we get to the point
where it seem that that is necessary we find a workaround. 
Right now, this is the ONLY issue we got.. 
  

> > 2. We're making a MPI library, and as such we don't have any control
> > with the application. 
> 
> LD_PRELOAD
> 

IN general LD_PRELOAD is fun for testing and academic programs, but not
for production code. 

In specific you run into a problem with how fortran 90 compilers do
dynamical arrays. It's very compiler dependent.  

> > 3c. It's therefore necessary for HW to access user pages.
> 
> Like TV cards do. That isnt hard
>  

nobody said it is. 

> > 4. In order to to 3, the user pages must be pinned down. 
> > 5. the way MPI is written, it's not using a special malloc() to allocate
> > the send receive buffers. It can't since it would break language binding
> > to fortran. Thus ANY writeable user page may be used.
> 
> Well not all the pages are guaranteed DMAable, so I guess you already
> lost.
>  

Nope. The drivers test to see if the page is DMAable, and do a copy if
necessary. Most of the high performance interconnects NIC's do 64 bit
PCI.  

> > 10. kernel patches are impractical, I must be able to do this with std
> > stock, redhat, AND suse kernels.   
> 
> So you want every vendor to screw up their kernels and the base kernel
> for an obscure (but fun) corner case. Thats not a rational choice is it.
> You want "performance is everything" you pay the price, don't make
> everyone suffer.

No! I don't disagree with removing the export of the syscall_table!

I just want the "proper mechanism" indicated by Arjan in the changelog.
Pls read this thread. There are legitimate uses to having syscall
hooks/notifications, either you think mine is or not.    

-- 
_________________________________________________________________________

Terje Eggestad                  mailto:terje.eggestad@scali.no
Scali Scalable Linux Systems    http://www.scali.com

Olaf Helsets Vei 6              tel:    +47 22 62 89 61 (OFFICE)
P.O.Box 150, Oppsal                     +47 975 31 574  (MOBILE)
N-0619 Oslo                     fax:    +47 22 62 89 51
NORWAY            
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