Re: [Linux-ia64] Re: Status on ioremap patch

From: Hugo Kohmann <>
Date: 2004-03-04 02:12:33

Is there any news or progress for official support for setting up kernel 
space write-combine mappings for Itanium systems. ?? Steffens patch is a 
good start, but we would like to avoid patching the kernel.

We are currently implementing a kernel space socket module for SCI 
(bypassing the TCP/IP protocols). Typical latency for send/receive 
between two systems is down to 2.7us for small messages ( Benchmarks 
running on Opterons ). Without kernel write-combine we would need to use 
regular DMA to move data, and we would no longer get the 2.7us latency.

Linux running on both IA32 and X86_64 systems supports some kind of kernel 
write-combine, why not IA64 ??

Best regards


>>>>>> On Wed, 09 Jan 2002 21:01:13 +0100, Steffen Persvold <> 
>  Steffen> So, what about this patch (posted earlier) David ? Have you
>  Steffen> seen the comments from Keith ?
>Keith's concerns are legitimate and to some degree apply even for
>ia64.  On ia64, we need to be careful to avoid mapping the same
>physical page with different memory attributes.  If more and more
>drivers are starting to use write-combine mappings, we need to solve
>this problem properly.  I don't have a solution off hand (I suspect
>we'll have to keep track of which i/o regions are mapped how) and
>don't have time to work on it now.  I'd recommend to maintain a
>separate patch for now, until a proper solution is ready (which will
>have to take non-ia64 platforms into consideration, of course).
>	--david
>PS: I apologize for not being as responsive yet as I'd like to be.
>    I'm done with the book (well, 99.999% as my wife put it...) and
>    ready to attack my backlog of kernel work (and other things, such
>    as user-level unwind support).  I just had a spell of bad luck
>    this week, which didn't help.  Hopefully, over the next one or two
>    weeks, things will start to go back to normal.


Hugo Kohmann                           |
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Received on Wed Mar 3 10:34:54 2004

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