[Xen-bugs] [Bug 1227] Out of SW-IOMMU space, 3ware Raid controller/3w-xxxx module

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http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=1227


fthain@xxxxxxxxxxxxxxxxxxx changed:

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------- Comment #9 from fthain@xxxxxxxxxxxxxxxxxxx  2011-10-13 04:44 -------
Hi Konrad,

Thanks for your response.

> I am pretty sure I responded to you on the mailing list. Did you read my reply
> there.
> 
> http://lists.xensource.com/archives/html/xen-devel/2011-09/msg00739.html

No, "Fantu" is someone else.

> So.. why are you not using the default values (64MB)

Using the default value crashed out on the x3550 when aacraid died (out of
SW-IOMMU space). The backtrace revealed that the problem was apparently DMA
buffer shortage. (So I don't see why this bug report is marked
"RESOLVED/INVALID".)

> I see you have  swiotlb=128 which ends up with:
> 
> DMA: Placing 0MB software IO TLB between ffff880020000000 - ffff880020040000
> DMA: software IO TLB at phys 0x20000000 - 0x20040000

I was wondering about that "0MB"...

> which of course means that there is not enough space. 0MB will
> cause issues like this. The parameter (if you look in the
> kernel-parameters.txt) defines it as -pages_, not megabytes.

I know, I already searched the kernel Documentation/ subdir before posting
here. It says,
"    swiotlb=<pages>[,force]
    <pages>            Prereserve that many 128K pages for the software IO
                       bounce buffering."

Of course, 128 * 128K = 16 MB not 0 MB... I never did figure that out.

> So either leave it as default, or change it to larger value, like 
> swiotlb=65535

Seems that the default isn't documented. Do you happen to know what it is?

I can try swiotlb=65535. I suppose this would yield about 512 MB. Assuming that
pages are in fact 8 K not 128 K. Is this correct?

Why did you subtract one from the power of two?


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