On Thu, Sep 28, 2017 at 07:16:12PM +1000, Alexey Kardashevskiy wrote: > Clearing very big IOMMU tables can trigger soft lockups. This adds > cond_resched() to allow the scheduler to do context switching when > it decides to. > > Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru>
Reviewed-by: David Gibson <da...@gibson.dropbear.id.au>
> ---
>
> The testcase is POWER9 box with 264GB guest, 4 VFIO devices from
> independent IOMMU groups, 64K IOMMU pages. This configuration produces
> 4325376 TCE entries, each entry update incurs 4 OPAL calls to update
> an individual PE TCE cache; this produced lockups for more than 20s.
> Reducing table size to 4194304 (i.e. 256GB guest) or removing one
> of 4 VFIO devices makes the problem go away.
>
> ---
> Changes:
> v3:
> * cond_resched() checks for should_resched() so we just call resched()
> and let the cpu scheduler decide whether to switch or not
>
> v2:
> * replaced with time based solution
> ---
> drivers/vfio/vfio_iommu_spapr_tce.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c
> b/drivers/vfio/vfio_iommu_spapr_tce.c
> index 63112c36ab2d..759a5bdd40e1 100644
> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> @@ -507,6 +507,8 @@ static int tce_iommu_clear(struct tce_container
> *container,
> enum dma_data_direction direction;
>
> for ( ; pages; --pages, ++entry) {
> + cond_resched();
> +
> direction = DMA_NONE;
> oldhpa = 0;
> ret = iommu_tce_xchg(tbl, entry, &oldhpa, &direction);
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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