Re: [PATCH v3] iommu/arm-smmu-v3: Shrink command/event/PRI queues in kdump kernel

[Nicolin Chen <nicolinc@nvidia.com>]

On Tue, Aug 04, 2026 at 01:59:05PM -0300, Jason Gunthorpe wrote:
> On Tue, Aug 04, 2026 at 09:45:01AM -0700, Nicolin Chen wrote:
> > On Tue, Aug 04, 2026 at 01:19:18PM -0300, Jason Gunthorpe wrote:
> > > On Tue, Aug 04, 2026 at 09:04:32AM -0700, Nicolin Chen wrote:
> > > > On Tue, Aug 04, 2026 at 11:17:04AM -0300, Jason Gunthorpe wrote:
> > > > > On Tue, Aug 04, 2026 at 03:02:46PM +0100, Will Deacon wrote:
> > > > > > > Would skipping their allocation when is_kdump_kernel() be acceptable on
> > > > > > > its own, or would you rather see it done differently?
> > > > > > 
> > > > > > With Nicolin's patch, we can just avoid allocating the priq and the evtq
> > > > > > entirely in the kdump case. We can then add a cmdline option to control
> > > > > > the maximum size of the cmdq, which is useful regardless of kdump.
> > > > > 
> > > > > I would still prefer kdump do this re-sizing automatically, even if we
> > > > > do add a commandline. It makes it easire to deploy than having to know
> > > > > secret command lines :\
> > > > > 
> > > > > So functionally I still think this patch is fine, though yes it points
> > > > > out more things in Nicolin's work too.
> > > > 
> > > > I will send a v10 of mine, to skip the EVTQ/PRIQ allocations.
> > > 
> > > I think Robin's point is to structure the v10 so you introduce a bunch
> > > of tunables, including something like 0 size to disable a feature.
> > >
> > > Then have kdump default those tunables to the right thing
> > 
> > But in kdump, EVTQ/PRIQ are disabled, so my series should have
> > skipped their allocations regardless of the tunables.
> > 
> > So, I think the tunables can be done in a separate series. And
> > its use case might not be confined to kdump?
> 
> I think the ask is to do the tunables first and change your series to
> default the tunables instead of doing direct kdump overrides.

You mean the driver can override the tunables to 0 in kdump mode,
right?

Well, we are skipping a lot of things in kdump mode already; it's
a very small change to skip EVTQ/PRIQ even without the tunables.

If Will prefers this merging sequence, I wouldn't mind changing my
series to overriding the tunables.

Thanks
Nicolin