Re: [Xen-devel] [Patch v11 1/3] IOMMU: add a timeout parameter for device IOTLB invalidation

["Xu, Quan" <quan.xu@xxxxxxxxx>]

On June 02, 2016 6:25 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
> >>> On 01.06.16 at 11:05, <quan.xu@xxxxxxxxx> wrote:
> > From: Quan Xu <quan.xu@xxxxxxxxx>
> > v11: Change the timeout parameter from 'vtd_qi_timeout' to
> >     'iommu_dev_iotlb_timeout', which is not only for VT-d device
> >     IOTLB invalidation, but also for other IOMMU implementations.
> 
> This goes after the first --- separator.
> 

Got it. It should be:

---
v11:
       - ...
       - ...
---


> > --- a/docs/misc/xen-command-line.markdown
> > +++ b/docs/misc/xen-command-line.markdown
> > @@ -996,6 +996,15 @@ debug hypervisor only).
> >
> >  >> Enable IOMMU debugging code (implies `verbose`).
> >
> > +### iommu\_dev\_iotlb\_timeout
> > +> `= <integer>`
> > +
> > +> Default: `1`
> 
> So on v10 I had made clear that any timeout reduction from its current value
> is, for the ATS case, not acceptable, unless you have proof that this lower
> value will fit all past, present, and future devices. Otherwise we're risking 
> a
> regression here.
> 

I really misunderstood the 'current value', which should be about 
'DMAR_OPERATION_TIMEOUT MILLISECS(1000) ', instead of ' IOMMU_QI_TIMEOUT 
MILLISECS(1)' in my patch.
So the default is 1000.
 
> > --- a/xen/drivers/passthrough/vtd/qinval.c
> > +++ b/xen/drivers/passthrough/vtd/qinval.c
> > @@ -28,6 +28,8 @@
> >  #include "vtd.h"
> >  #include "extern.h"
> >
> > +#define IOMMU_QI_TIMEOUT MILLISECS(1)
> 
> May I suggest VTD_QI_TIMEOUT (but see also below)?
> 

Agreed. VTD_QI_TIMEOUT is a better one.

> > @@ -163,14 +165,21 @@ static int queue_invalidate_wait(struct iommu
> *iommu,
> >      /* Now we don't support interrupt method */
> >      if ( sw )
> >      {
> > +        s_time_t timeout;
> > +
> >          /* In case all wait descriptor writes to same addr with same data 
> > */
> > -        start_time = NOW();
> > +        timeout = flush_dev_iotlb ?
> > +                  (NOW() + iommu_dev_iotlb_timeout * MILLISECS(1)) :
> 
> MILLISECS(iommu_dev_iotlb_timeout)
> 
> > +                  (NOW() + IOMMU_QI_TIMEOUT);
> 
> Or really the whole expression should probably simply become
> 
>         timeout = NOW() + MILLISECS(flush_dev_iotlb ?
> iommu_dev_iotlb_timeout : VTD_QI_TIMEOUT);
> 
> (of course with VTD_QI_TIMEOUT having its MILLISECS() dropped, and
> suitably line wrapped).
> 


I prefer this later one.

Quan
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