lkml.org 
[lkml]   [2012]   [Dec]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v7 24/27] x86: Add swiotlb force off support
On Fri, Dec 21, 2012 at 07:23:03PM -0800, Eric W. Biederman wrote:
> Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> writes:
>
> > On Fri, Dec 21, 2012 at 06:42:47PM -0800, Eric W. Biederman wrote:
> >> Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> writes:
> >>
> >> > On Mon, Dec 17, 2012 at 11:15:56PM -0800, Yinghai Lu wrote:
> >> >> So use could disable swiotlb from command line, even swiotlb support
> >> >> is compiled in. Just like we have intel_iommu=on and intel_iommu=off.
> >> >
> >> > You really need to spell out why this is useful.
> >>
> >> YH why can't we safely autodetect that the swiotlb is unusable when
> >> there is no memory below 4G free?
> >
> > I am not sure what 'YH' stands for (Yeah?).
>
> Yinghai Lu's nickname.
>
> > However we could turn SWIOTLB off altogether if it cannot allocate
> > _some_ memory. It could try first 64MB, then 32MB, lastly 16MB. And
> > if all that fails - print a nice warning and continue on.
> >
> > Later in the late initialization phase, when pci_swiotlb_late_init
> > is called - it can then figure out whether 'iommu' has been set
> > and it iself was never able to allocate. At that point it can try
> > the dynamic allocation (swiotlb_late_init_with_default_size)
> > ... and if that fails give up and panic.
>
> As far as I can tell panics should be avoided unless there is something
> that actually needs an iommu, and the swiommu is the only option, and
> the swiommu can not fulfill that request.

Right.
>
> In this case YH has been working on the case of loading a kernel
> completely above 4G, and apparently he has also been testing the case of
> running a kernel with no memory below 4G.
>
> Eric
>


\
 
 \ /
  Last update: 2012-12-22 15:01    [W:0.046 / U:4.660 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site