[RESEND,3/3] iommu/dma: Plumb in the per-CPU IOVA caches
Robin Murphy
robin.murphy at arm.com
Thu Apr 6 14:56:16 EDT 2017
On 06/04/17 19:15, Manoj Iyer wrote:
> On Fri, 31 Mar 2017, Robin Murphy wrote:
>
>> With IOVA allocation suitably tidied up, we are finally free to opt in
>> to the per-CPU caching mechanism. The caching alone can provide a modest
>> improvement over walking the rbtree for weedier systems (iperf3 shows
>> ~10% more ethernet throughput on an ARM Juno r1 constrained to a single
>> 650MHz Cortex-A53), but the real gain will be in sidestepping the rbtree
>> lock contention which larger ARM-based systems with lots of parallel I/O
>> are starting to feel the pain of.
>>
>> Reviewed-by: Nate Watterson <nwatters at codeaurora.org>
>> Tested-by: Nate Watterson <nwatters at codeaurora.org>
>> Signed-off-by: Robin Murphy <robin.murphy at arm.com>
>> ---
>> drivers/iommu/dma-iommu.c | 39 ++++++++++++++++++---------------------
>> 1 file changed, 18 insertions(+), 21 deletions(-)
>>
>> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
>> index 1b94beb43036..8348f366ddd1 100644
>> --- a/drivers/iommu/dma-iommu.c
>> +++ b/drivers/iommu/dma-iommu.c
>> @@ -361,8 +361,7 @@ static dma_addr_t iommu_dma_alloc_iova(struct
>> iommu_domain *domain,
>> {
>> struct iommu_dma_cookie *cookie = domain->iova_cookie;
>> struct iova_domain *iovad = &cookie->iovad;
>> - unsigned long shift, iova_len;
>> - struct iova *iova = NULL;
>> + unsigned long shift, iova_len, iova = 0;
>>
>> if (cookie->type == IOMMU_DMA_MSI_COOKIE) {
>> cookie->msi_iova += size;
>> @@ -371,41 +370,39 @@ static dma_addr_t iommu_dma_alloc_iova(struct
>> iommu_domain *domain,
>>
>> shift = iova_shift(iovad);
>> iova_len = size >> shift;
>> + /*
>> + * Freeing non-power-of-two-sized allocations back into the IOVA
>> caches
>> + * will come back to bite us badly, so we have to waste a bit of
>> space
>> + * 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)))
>> + iova_len = roundup_pow_of_two(iova_len);
>>
>> if (domain->geometry.force_aperture)
>> dma_limit = min(dma_limit, domain->geometry.aperture_end);
>>
>> /* Try to get PCI devices a SAC address */
>> if (dma_limit > DMA_BIT_MASK(32) && dev_is_pci(dev))
>> - iova = alloc_iova(iovad, iova_len, DMA_BIT_MASK(32) >> shift,
>> - true);
>> - /*
>> - * Enforce size-alignment to be safe - there could perhaps be an
>> - * attribute to control this per-device, or at least per-domain...
>> - */
>> - if (!iova)
>> - iova = alloc_iova(iovad, iova_len, dma_limit >> shift, true);
>> + iova = alloc_iova_fast(iovad, iova_len, DMA_BIT_MASK(32) >>
>> shift);
>>
>> - return (dma_addr_t)iova->pfn_lo << shift;
>> + if (!iova)
>> + iova = alloc_iova_fast(iovad, iova_len, dma_limit >> shift);
>> +
>> + return (dma_addr_t)iova << shift;
>> }
>>
>> static void iommu_dma_free_iova(struct iommu_dma_cookie *cookie,
>> dma_addr_t iova, size_t size)
>> {
>> struct iova_domain *iovad = &cookie->iovad;
>> - struct iova *iova_rbnode;
>> + unsigned long shift = iova_shift(iovad);
>>
>> /* The MSI case is only ever cleaning up its most recent
>> allocation */
>> - if (cookie->type == IOMMU_DMA_MSI_COOKIE) {
>> + if (cookie->type == IOMMU_DMA_MSI_COOKIE)
>> cookie->msi_iova -= size;
>> - return;
>> - }
>> -
>> - iova_rbnode = find_iova(iovad, iova_pfn(iovad, iova));
>> - if (WARN_ON(!iova_rbnode))
>> - return;
>> -
>> - __free_iova(iovad, iova_rbnode);
>> + else
>> + free_iova_fast(iovad, iova >> shift, size >> shift);
>> }
>>
>> static void __iommu_dma_unmap(struct iommu_domain *domain, dma_addr_t
>> dma_addr,
>>
>
> This patch series helps to resolve the Ubuntu bug, where we see the
> Ubuntu Zesty (4.10 based) kernel reporting multi cpu soft lockups on
> QDF2400 SDP. https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1680549
Wow, how many separate buffers does that driver have mapped at once to
spend 22 seconds walking the rbtree for a single allocation!? I'd almost
expect that to indicate a deadlock.
I'm guessing you wouldn't have seen this on older kernels, since I
assume that particular platform is booting via ACPI, so wouldn't have
had the SMMU enabled without the IORT support which landed in 4.10.
> This patch series along with the following cherry-picks from Linus's tree
> dddd632b072f iommu/dma: Implement PCI allocation optimisation
> de84f5f049d9 iommu/dma: Stop getting dma_32bit_pfn wrong
>
> were applied to Ubuntu Zesty 4.10 kernel (Ubuntu-4.10.0-18.20) and
> tested on a QDF2400 SDP.
>
> Tested-by: Manoj Iyer <manoj.iyer at canonical.com>
Thanks,
Robin.
>
>
> --
> ============================
> Manoj Iyer
> Ubuntu/Canonical
> ARM Servers - Cloud
> ============================
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