From: Nikita Danilov <nikita@clusterfs.com>
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Date: Tue, 4 Oct 2005 21:40:27 +0400
To: Luke Kenneth Casson Leighton <lkcl@lkcl.net>
Cc: "Martin J. Bligh" <mbligh@mbligh.org>, Rik van Riel <riel@redhat.com>,
       linux-kernel@vger.kernel.org
Subject: Re: what's next for the linux kernel?
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Luke Kenneth Casson Leighton writes:
 > On Tue, Oct 04, 2005 at 09:15:57PM +0400, Nikita Danilov wrote:
 > > Luke Kenneth Casson Leighton writes:
 > > 
 > > [...]
 > > 
 > >  > 
 > >  >  assuming that you have an intelligent programmer (or some really good
 > >  >  and working parallelisation tools) who really knows his threads?
 > > 
 > > Well, I'd like to have a hardware with CAS-n operation for one
 > > thing. 
 > 
 >  CAS - compare and swap - by CAS-n i presume that you mean effectively a
 >  SIMD CAS instruction?

An instruction that atomically compares and swaps n independent memory
locations with n given values. cas-1 (traditional compare-and-swap) is
enough to implement lock-less queue, cas-2 is enough to implement
double-linked lists, and was used by Synthesis lock-free kernel
(http://citeseer.ist.psu.edu/massalin91lockfree.html).

To be precise, cas-1 is theoretically enough to implement double-linked
lists too, but resulting algorithms are not pretty at all.

 > 
 > > But what would this buy us? 
 > 
 >  you do not say :)  i am genuinely interested to hear what it would buy.

Nothing. That was an instance of "rhetorical question", sorry that I
made not this clear enough.

 > 
 > > Having different kernel algorithms
 > > for x86 and mythical cas-n-able hardware is not viable.
 > 
 >  if i can get an NPTL .deb package for glibc for x86 only it would tend
 >  to imply that that isn't a valid conclusion: am i missing something?

Yes: this is Linux _Kernel_ mailing list, and I was talking about kernel
code and kernel algorithms.

 > 
 >  cheers,
 > 
 >  l.
 >  

Nikita.

 >  
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