Re: [PATCH v4] iommu: Optimise PCI SAC address trick

[John Garry]

On 13/06/2023 18:58, Jakub Kicinski wrote:
> On Fri, 14 Apr 2023 13:45:34 +0200 Joerg Roedel wrote:
> > Thanks for working on this, I think this is good to go. But given the
> > issues we had with last attempt I'd like to have this in linux-next for
> > a few weeks before sending it upstream. Therefore I will defer this
> > patch and merge it early in the next cycle.
> Is this patch queued up? I don't see it in linux-next and we keep
> hitting this issue in production. After a few NIC reconfigurations
> IOMMU starts consuming 90+% of CPU time.

Since we're at rc6 time and a cautious approach was wanted to merge this 
change, I doubt that this will be merged for this cycle. That's quite 
unfortunate.

Please note what I mentioned earlier about using dma_opt_mapping_size(). 
This API is used by some block storage drivers to avoid your same 
problem, by clamping max_sectors_kb at this size - see sysfs-block Doc 
for info there. Maybe it can be used similarly for network drivers.

Thanks,
John