Messages in this thread | | | Subject | Re: [PATCH v4 2/6] iova: Allow rcache range upper limit to be flexible | From | John Garry <> | Date | Mon, 2 Aug 2021 16:23:00 +0100 |
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On 02/08/2021 16:01, Will Deacon wrote: > On Wed, Jul 14, 2021 at 06:36:39PM +0800, John Garry wrote: >> Some LLDs may request DMA mappings whose IOVA length exceeds that of the >> current rcache upper limit. > > What's an LLD? >
low-level driver
maybe I'll stick with simply "drivers"
>> 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. >> >> [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/dma-iommu.c | 2 +- >> drivers/iommu/iova.c | 23 +++++++++++++++++------ >> include/linux/iova.h | 4 ++-- >> 3 files changed, 20 insertions(+), 9 deletions(-) >> >> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c >> index 98ba927aee1a..4772278aa5da 100644 >> --- a/drivers/iommu/dma-iommu.c >> +++ b/drivers/iommu/dma-iommu.c >> @@ -434,7 +434,7 @@ static dma_addr_t iommu_dma_alloc_iova(struct iommu_domain *domain, >> * rounding up anything cacheable to make sure that can't happen. The >> * order of the unadjusted size will still match upon freeing. >> */ >> - if (iova_len < (1 << (IOVA_RANGE_CACHE_MAX_SIZE - 1))) >> + if (iova_len < (1 << (iovad->rcache_max_size - 1))) >> iova_len = roundup_pow_of_two(iova_len); >> >> dma_limit = min_not_zero(dma_limit, dev->bus_dma_limit); >> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c >> index b6cf5f16123b..07ce73fdd8c1 100644 >> --- a/drivers/iommu/iova.c >> +++ b/drivers/iommu/iova.c >> @@ -15,6 +15,8 @@ >> /* 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) */ > > Is that the same as an 'order'? i.e. IOVA_RANGE_CACHE_MAX_ORDER?
Yeah, that may be better. I was just using the same name as before.
> >> + >> static bool iova_rcache_insert(struct iova_domain *iovad, >> unsigned long pfn, >> unsigned long size); >> @@ -881,7 +883,14 @@ static void init_iova_rcaches(struct iova_domain *iovad) >> unsigned int cpu; >> int i; >> >> - for (i = 0; i < IOVA_RANGE_CACHE_MAX_SIZE; ++i) { >> + iovad->rcache_max_size = IOVA_RANGE_CACHE_MAX_SIZE; >> + >> + iovad->rcaches = kcalloc(iovad->rcache_max_size, >> + sizeof(*iovad->rcaches), GFP_KERNEL); >> + if (!iovad->rcaches) >> + return; > > Returning quietly here doesn't seem like the right thing to do. At least, I > don't think the rest of the functions here are checking rcaches against > NULL. >
For sure, but that is what other code which can fail here already does, like:
static void init_iova_rcaches(struct iova_domain *iovad) { ...
for (i = 0; i < IOVA_RANGE_CACHE_MAX_SIZE; ++i) { ...
rcache->cpu_rcaches = __alloc_percpu(sizeof(*cpu_rcache), cache_line_size()); if (WARN_ON(!rcache->cpu_rcaches)) continue; }
and that is not safe either.
This issue was raised a while ago. I don't mind trying to fix it - a slightly painful part is that it touches a few subsystems.
Thanks, John
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