Will Deacon
2022-Jul-06 12:11 UTC
[PATCH RESEND v5 2/5] iova: Allow rcache range upper limit to be flexible
On Thu, Apr 07, 2022 at 03:52:53PM +0800, Leizhen (ThunderTown) wrote:> On 2022/4/4 19:27, John Garry wrote: > > Some low-level drivers may request DMA mappings whose IOVA length exceeds > > that of the current rcache upper limit. > > > > This means that allocations for those IOVAs will never be cached, and > > always must be allocated and freed from the RB tree per DMA mapping cycle. > > This has a significant effect on performance, more so since commit > > 4e89dce72521 ("iommu/iova: Retry from last rb tree node if iova search > > fails"), as discussed at [0]. > > > > As a first step towards allowing the rcache range upper limit be > > configured, hold this value in the IOVA rcache structure, and allocate > > the rcaches separately. > > > > Delete macro IOVA_RANGE_CACHE_MAX_SIZE in case it's reused by mistake. > > > > [0] https://lore.kernel.org/linux-iommu/20210129092120.1482-1-thunder.leizhen at huawei.com/ > > > > Signed-off-by: John Garry <john.garry at huawei.com> > > --- > > drivers/iommu/iova.c | 20 ++++++++++---------- > > include/linux/iova.h | 3 +++ > > 2 files changed, 13 insertions(+), 10 deletions(-) > > > > diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c > > index db77aa675145..5c22b9187b79 100644 > > --- a/drivers/iommu/iova.c > > +++ b/drivers/iommu/iova.c > > @@ -15,8 +15,6 @@ > > /* The anchor node sits above the top of the usable address space */ > > #define IOVA_ANCHOR ~0UL > > > > -#define IOVA_RANGE_CACHE_MAX_SIZE 6 /* log of max cached IOVA range size (in pages) */ > > - > > static bool iova_rcache_insert(struct iova_domain *iovad, > > unsigned long pfn, > > unsigned long size); > > @@ -443,7 +441,7 @@ alloc_iova_fast(struct iova_domain *iovad, unsigned long size, > > * rounding up anything cacheable to make sure that can't happen. The > > * order of the unadjusted size will still match upon freeing. > > */ > > - if (size < (1 << (IOVA_RANGE_CACHE_MAX_SIZE - 1))) > > + if (size < (1 << (iovad->rcache_max_size - 1))) > > size = roundup_pow_of_two(size); > > > > iova_pfn = iova_rcache_get(iovad, size, limit_pfn + 1); > > @@ -713,13 +711,15 @@ int iova_domain_init_rcaches(struct iova_domain *iovad) > > unsigned int cpu; > > int i, ret; > > > > - iovad->rcaches = kcalloc(IOVA_RANGE_CACHE_MAX_SIZE, > > + iovad->rcache_max_size = 6; /* Arbitrarily high default */ > > It would be better to assign this constant value to iovad->rcache_max_size > in init_iova_domain().I think it's fine where it is as it's a meaningless number outside of the rcache code. Will