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

Hugo Kohmann
2004-03-03T15:12:33Z

Hi,

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

Hugo

>>>>>> On Wed, 09 Jan 2002 21:01:13 +0100, Steffen Persvold <sp@scali.no>
>said:
>
> 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.

--

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