Re: [PATCH rc] iommupt: Only cache flush memory changed by unmap

[Baolu Lu <baolu.lu@linux.intel.com>]

On 1/25/26 05:00, Jason Gunthorpe wrote:
> The cache flush was happening on every level across the whole range of
> iteration, even if no leafs or tables were cleared. Instead flush only the
> sub range that was actually written.
> 
> Overflushing isn't a correctness problem but it does impact the
> performance of unmap.
> 
> After this series the performance compared to the original VT-d
> implementation with cache flushing turned on is:
> 
> map_pages
>     pgsz  ,avg new,old ns, min new,old ns  , min % (+ve is better)
>       2^12,    253,266   ,     213,227     ,   6.06
>       2^21,    246,244   ,     221,219     ,   0.00
>       2^30,    231,240   ,     209,217     ,   3.03
>   256*2^12,   2604,2668  ,    2415,2540    ,   4.04
>   256*2^21,   2495,2824  ,    2390,2734    ,  12.12
>   256*2^30,   2542,2845  ,    2380,2718    ,  12.12
> 
> unmap_pages
>     pgsz  ,avg new,old ns, min new,old ns  , min % (+ve is better)
>       2^12,    259,292   ,     222,251     ,  11.11
>       2^21,    255,259   ,     227,236     ,   3.03
>       2^30,    238,254   ,     217,230     ,   5.05
>   256*2^12,   2751,2620  ,    2417,2437    ,   0.00
>   256*2^21,   2461,2526  ,    2377,2423    ,   1.01
>   256*2^30,   2498,2543  ,    2370,2404    ,   1.01
> 
> Fixes: efa03dab7ce4 ("iommupt: Flush the CPU cache after any writes to the page table")
> Reported-by: Francois Dugast<francois.dugast@intel.com>
> Closes:https://lore.kernel.org/all/20260121130233.257428-1- 
> francois.dugast@intel.com/
> Signed-off-by: Jason Gunthorpe<jgg@nvidia.com>
> ---
>   drivers/iommu/generic_pt/iommu_pt.h | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)

Thanks for fixing this.

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>