Messages in this thread | | | Subject | Re: [PATCH 3/6] iova: Allow rcache range upper limit to be configurable | From | Robin Murphy <> | Date | Fri, 19 Mar 2021 16:25:39 +0000 |
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On 2021-03-19 13:25, John Garry wrote: > Some LLDs 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]. > > Allow the range of cached IOVAs to be increased, by providing an API to set > the upper limit, which is capped at IOVA_RANGE_CACHE_MAX_SIZE. > > For simplicity, the full range of IOVA rcaches is allocated and initialized > at IOVA domain init time. > > Setting the range upper limit will fail if the domain is already live > (before the tree contains IOVA nodes). This must be done to ensure any > IOVAs cached comply with rule of size being a power-of-2. > > [0] https://lore.kernel.org/linux-iommu/20210129092120.1482-1-thunder.leizhen@huawei.com/ > > Signed-off-by: John Garry <john.garry@huawei.com> > --- > drivers/iommu/iova.c | 37 +++++++++++++++++++++++++++++++++++-- > include/linux/iova.h | 11 ++++++++++- > 2 files changed, 45 insertions(+), 3 deletions(-) > > diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c > index cecc74fb8663..d4f2f7fbbd84 100644 > --- a/drivers/iommu/iova.c > +++ b/drivers/iommu/iova.c > @@ -49,6 +49,7 @@ init_iova_domain(struct iova_domain *iovad, unsigned long granule, > iovad->flush_cb = NULL; > iovad->fq = NULL; > iovad->anchor.pfn_lo = iovad->anchor.pfn_hi = IOVA_ANCHOR; > + iovad->rcache_max_size = IOVA_RANGE_CACHE_DEFAULT_SIZE; > rb_link_node(&iovad->anchor.node, NULL, &iovad->rbroot.rb_node); > rb_insert_color(&iovad->anchor.node, &iovad->rbroot); > init_iova_rcaches(iovad); > @@ -194,7 +195,7 @@ static int __alloc_and_insert_iova_range(struct iova_domain *iovad, > * rounding up anything cacheable to make sure that can't happen. The > * order of the unadjusted size will still match upon freeing. > */ > - if (fast && size < (1 << (IOVA_RANGE_CACHE_MAX_SIZE - 1))) > + if (fast && size < (1 << (iovad->rcache_max_size - 1))) > size = roundup_pow_of_two(size); > > if (size_aligned) > @@ -901,7 +902,7 @@ static bool iova_rcache_insert(struct iova_domain *iovad, unsigned long pfn, > { > unsigned int log_size = order_base_2(size); > > - if (log_size >= IOVA_RANGE_CACHE_MAX_SIZE) > + if (log_size >= iovad->rcache_max_size) > return false; > > return __iova_rcache_insert(iovad, &iovad->rcaches[log_size], pfn); > @@ -946,6 +947,38 @@ static unsigned long __iova_rcache_get(struct iova_rcache *rcache, > return iova_pfn; > } > > +void iova_rcache_set_upper_limit(struct iova_domain *iovad, > + unsigned long iova_len) > +{ > + unsigned int rcache_index = order_base_2(iova_len) + 1; > + struct rb_node *rb_node = &iovad->anchor.node; > + unsigned long flags; > + int count = 0; > + > + spin_lock_irqsave(&iovad->iova_rbtree_lock, flags); > + if (rcache_index <= iovad->rcache_max_size) > + goto out; > + > + while (1) { > + rb_node = rb_prev(rb_node); > + if (!rb_node) > + break; > + count++; > + } > + > + /* > + * If there are already IOVA nodes present in the tree, then don't > + * allow range upper limit to be set. > + */ > + if (count != iovad->reserved_node_count) > + goto out; > + > + iovad->rcache_max_size = min_t(unsigned long, rcache_index, > + IOVA_RANGE_CACHE_MAX_SIZE); > +out: > + spin_unlock_irqrestore(&iovad->iova_rbtree_lock, flags); > +} > + > /* > * Try to satisfy IOVA allocation range from rcache. Fail if requested > * size is too big or the DMA limit we are given isn't satisfied by the > diff --git a/include/linux/iova.h b/include/linux/iova.h > index fd3217a605b2..952b81b54ef7 100644 > --- a/include/linux/iova.h > +++ b/include/linux/iova.h > @@ -25,7 +25,8 @@ struct iova { > struct iova_magazine; > struct iova_cpu_rcache; > > -#define IOVA_RANGE_CACHE_MAX_SIZE 6 /* log of max cached IOVA range size (in pages) */ > +#define IOVA_RANGE_CACHE_DEFAULT_SIZE 6 > +#define IOVA_RANGE_CACHE_MAX_SIZE 10 /* log of max cached IOVA range size (in pages) */
No.
And why? If we're going to allocate massive caches anyway, whatever is the point of *not* using all of them?
It only makes sense for a configuration knob to affect the actual rcache and depot allocations - that way, big high-throughput systems with plenty of memory can spend it on better performance, while small systems - that often need IOMMU scatter-gather precisely *because* memory is tight and thus easily fragmented - don't have to pay the (not insignificant) cost for caches they don't need.
Robin.
> #define MAX_GLOBAL_MAGS 32 /* magazines per bin */ > > struct iova_rcache { > @@ -74,6 +75,7 @@ struct iova_domain { > unsigned long start_pfn; /* Lower limit for this domain */ > unsigned long dma_32bit_pfn; > unsigned long max32_alloc_size; /* Size of last failed allocation */ > + unsigned long rcache_max_size; /* Upper limit of cached IOVA RANGE */ > struct iova_fq __percpu *fq; /* Flush Queue */ > > atomic64_t fq_flush_start_cnt; /* Number of TLB flushes that > @@ -158,6 +160,8 @@ int init_iova_flush_queue(struct iova_domain *iovad, > struct iova *find_iova(struct iova_domain *iovad, unsigned long pfn); > void put_iova_domain(struct iova_domain *iovad); > void free_cpu_cached_iovas(unsigned int cpu, struct iova_domain *iovad); > +void iova_rcache_set_upper_limit(struct iova_domain *iovad, > + unsigned long iova_len); > #else > static inline int iova_cache_get(void) > { > @@ -238,6 +242,11 @@ static inline void free_cpu_cached_iovas(unsigned int cpu, > struct iova_domain *iovad) > { > } > + > +static inline void iova_rcache_set_upper_limit(struct iova_domain *iovad, > + unsigned long iova_len) > +{ > +} > #endif > > #endif >
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