Re: [Xen-devel] [linux-linus test] 25478: regressions - FAIL [and 1 more messages]

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Apr 16, 2014 at 01:06:06PM +0100, Ian Jackson wrote:
> Konrad Rzeszutek Wilk writes ("Re: [Xen-devel] [linux-linus test] 25478: 
> regressions - FAIL [and 1 more messages]"):
> > On Apr 16, 2014 6:12 AM, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx> wrote:
> > > Another week has gone by and Linux tip still fails this test.
> > 
> > Did you try the recommendation that David offered - boot with 4GB to dom0?
> 
> That would be a workaround.  I can do that (as it happens these
> machines have 8G of RAM so it is actually possible), but:

Right.
> 
> The purpose of running tests is to discover bugs (so that they can be
> fixed).  It is not to generate a nice clean report by sweeping things
> under the carpet.

Right.
> 
> Here the tests have discovered a bug in Linux.  AIUI it's a bug which
> is visible when using this particular driver, but which is actually a
> problem with the Xen integration into the Linux VM system in general.
> So other it presumably affects other drivers too.  It should be fixed,
> not worked around.

I concur.
> 
> The downside of not working around this bug is that osstest's
> failing-host-stickiness will cause an increasing proportion of the
> tests to run on the affected hosts.  This might mask other bugs.
> 
> Conversely, working around this bug in the manner suggested will
> presumably just make the bug disappear off our radar.

There is a danger of that.

I am not going to be able to take a look at this bug in the next three 
weeks. If anybody else wants to take a stab at this - here is my hand-waving
idea of how it could be done:

1). Cleanup the ia64 usage of same code 'ia64_dma_get_required_mask'
    (it actually duplicates what the drivers/base has). Perhaps move it to
    lib/iommu-helper.c
    Call it 'generic_get_required_mask' or such. 
2). Look at other platforms that use a similar (or the same) code
    and see if they can re-use it now that it is in lib/iommu-helper.c.
3). Make the x86 dma_ops start using the extra "get_required_mask"
    and point it to the generic_get_required_mask.
4). Make the xen-swiotlb use its own version. 

> 
> Ian.

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