diff mbox series

[V3] iommu: Optimize IOMMU UnMap

Message ID 20240805084106.214584-1-amhetre@nvidia.com
State Changes Requested
Headers show
Series [V3] iommu: Optimize IOMMU UnMap | expand

Commit Message

Ashish Mhetre Aug. 5, 2024, 8:41 a.m. UTC
The current __arm_lpae_unmap() function calls dma_sync() on individual
PTEs after clearing them. Overall unmap performance can be improved by
around 25% for large buffer sizes by combining the syncs for adjacent
leaf entries.
Optimize the unmap time by clearing all the leaf entries and issuing a
single dma_sync() for them.
Below is detailed analysis of average unmap latency(in us) with and
without this optimization obtained by running dma_map_benchmark for
different buffer sizes.

		UnMap Latency(us)
Size	Without		With		% gain with
	optimiztion	optimization	optimization

4KB	3		3		0
8KB	4		3.8		5
16KB	6.1		5.4		11.48
32KB	10.2		8.5		16.67
64KB	18.5		14.9		19.46
128KB	35		27.5		21.43
256KB	67.5		52.2		22.67
512KB	127.9		97.2		24.00
1MB	248.6		187.4		24.62
2MB	65.5		65.5		0
4MB	119.2		119		0.17

Signed-off-by: Ashish Mhetre <amhetre@nvidia.com>
---
Changes in V2:
- Updated the commit message to be imperative.
- Fixed ptep at incorrect index getting cleared for non-leaf entries.

Changes in V3:
- Used loop-local variables and removed redundant function variables.
- Added check for zero-sized dma_sync in __arm_lpae_clear_pte().
- Merged both patches into this single patch by adding check for a
  NULL gather in __arm_lpae_unmap() itself.
---
 drivers/iommu/io-pgtable-arm.c | 31 +++++++++++++++++--------------
 1 file changed, 17 insertions(+), 14 deletions(-)

Comments

Robin Murphy Aug. 6, 2024, 10:39 a.m. UTC | #1
On 05/08/2024 9:41 am, Ashish Mhetre wrote:
> The current __arm_lpae_unmap() function calls dma_sync() on individual
> PTEs after clearing them. Overall unmap performance can be improved by
> around 25% for large buffer sizes by combining the syncs for adjacent
> leaf entries.
> Optimize the unmap time by clearing all the leaf entries and issuing a
> single dma_sync() for them.
> Below is detailed analysis of average unmap latency(in us) with and
> without this optimization obtained by running dma_map_benchmark for
> different buffer sizes.
> 
> 		UnMap Latency(us)
> Size	Without		With		% gain with
> 	optimiztion	optimization	optimization
> 
> 4KB	3		3		0
> 8KB	4		3.8		5
> 16KB	6.1		5.4		11.48
> 32KB	10.2		8.5		16.67
> 64KB	18.5		14.9		19.46
> 128KB	35		27.5		21.43
> 256KB	67.5		52.2		22.67
> 512KB	127.9		97.2		24.00
> 1MB	248.6		187.4		24.62
> 2MB	65.5		65.5		0
> 4MB	119.2		119		0.17
> 
> Signed-off-by: Ashish Mhetre <amhetre@nvidia.com>
> ---
> Changes in V2:
> - Updated the commit message to be imperative.
> - Fixed ptep at incorrect index getting cleared for non-leaf entries.
> 
> Changes in V3:
> - Used loop-local variables and removed redundant function variables.
> - Added check for zero-sized dma_sync in __arm_lpae_clear_pte().
> - Merged both patches into this single patch by adding check for a
>    NULL gather in __arm_lpae_unmap() itself.

Yeah, that's cleaned up really nicely!

Other than a nit that the subject ideally wants to be something more 
accurate like "iommu/io-pgtable-arm: Optimise non-coherent unmap" (sorry 
I forgot to mention that last time),

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> ---
>   drivers/iommu/io-pgtable-arm.c | 31 +++++++++++++++++--------------
>   1 file changed, 17 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
> index f5d9fd1f45bf..6fecf3d9fe67 100644
> --- a/drivers/iommu/io-pgtable-arm.c
> +++ b/drivers/iommu/io-pgtable-arm.c
> @@ -274,13 +274,13 @@ static void __arm_lpae_sync_pte(arm_lpae_iopte *ptep, int num_entries,
>   				   sizeof(*ptep) * num_entries, DMA_TO_DEVICE);
>   }
>   
> -static void __arm_lpae_clear_pte(arm_lpae_iopte *ptep, struct io_pgtable_cfg *cfg)
> +static void __arm_lpae_clear_pte(arm_lpae_iopte *ptep, struct io_pgtable_cfg *cfg, int num_entries)
>   {
> +	for (int i = 0; i < num_entries; i++)
> +		ptep[i] = 0;
>   
> -	*ptep = 0;
> -
> -	if (!cfg->coherent_walk)
> -		__arm_lpae_sync_pte(ptep, 1, cfg);
> +	if (!cfg->coherent_walk && num_entries)
> +		__arm_lpae_sync_pte(ptep, num_entries, cfg);
>   }
>   
>   static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
> @@ -654,26 +654,29 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
>   		max_entries = ARM_LPAE_PTES_PER_TABLE(data) - unmap_idx_start;
>   		num_entries = min_t(int, pgcount, max_entries);
>   
> -		while (i < num_entries) {
> -			pte = READ_ONCE(*ptep);
> +		/* Find and handle non-leaf entries */
> +		for (i = 0; i < num_entries; i++) {
> +			pte = READ_ONCE(ptep[i]);
>   			if (WARN_ON(!pte))
>   				break;
>   
> -			__arm_lpae_clear_pte(ptep, &iop->cfg);
> -
>   			if (!iopte_leaf(pte, lvl, iop->fmt)) {
> +				__arm_lpae_clear_pte(&ptep[i], &iop->cfg, 1);
> +
>   				/* Also flush any partial walks */
>   				io_pgtable_tlb_flush_walk(iop, iova + i * size, size,
>   							  ARM_LPAE_GRANULE(data));
>   				__arm_lpae_free_pgtable(data, lvl + 1, iopte_deref(pte, data));
> -			} else if (!iommu_iotlb_gather_queued(gather)) {
> -				io_pgtable_tlb_add_page(iop, gather, iova + i * size, size);
>   			}
> -
> -			ptep++;
> -			i++;
>   		}
>   
> +		/* Clear the remaining entries */
> +		__arm_lpae_clear_pte(ptep, &iop->cfg, i);
> +
> +		if (gather && !iommu_iotlb_gather_queued(gather))
> +			for (int j = 0; j < i; j++)
> +				io_pgtable_tlb_add_page(iop, gather, iova + j * size, size);
> +
>   		return i * size;
>   	} else if (iopte_leaf(pte, lvl, iop->fmt)) {
>   		/*
Ashish Mhetre Aug. 6, 2024, 10:43 a.m. UTC | #2
On 8/6/2024 4:09 PM, Robin Murphy wrote:
> External email: Use caution opening links or attachments
>
>
> On 05/08/2024 9:41 am, Ashish Mhetre wrote:
>> The current __arm_lpae_unmap() function calls dma_sync() on individual
>> PTEs after clearing them. Overall unmap performance can be improved by
>> around 25% for large buffer sizes by combining the syncs for adjacent
>> leaf entries.
>> Optimize the unmap time by clearing all the leaf entries and issuing a
>> single dma_sync() for them.
>> Below is detailed analysis of average unmap latency(in us) with and
>> without this optimization obtained by running dma_map_benchmark for
>> different buffer sizes.
>>
>>               UnMap Latency(us)
>> Size  Without         With            % gain with
>>       optimiztion     optimization    optimization
>>
>> 4KB   3               3               0
>> 8KB   4               3.8             5
>> 16KB  6.1             5.4             11.48
>> 32KB  10.2            8.5             16.67
>> 64KB  18.5            14.9            19.46
>> 128KB 35              27.5            21.43
>> 256KB 67.5            52.2            22.67
>> 512KB 127.9           97.2            24.00
>> 1MB   248.6           187.4           24.62
>> 2MB   65.5            65.5            0
>> 4MB   119.2           119             0.17
>>
>> Signed-off-by: Ashish Mhetre <amhetre@nvidia.com>
>> ---
>> Changes in V2:
>> - Updated the commit message to be imperative.
>> - Fixed ptep at incorrect index getting cleared for non-leaf entries.
>>
>> Changes in V3:
>> - Used loop-local variables and removed redundant function variables.
>> - Added check for zero-sized dma_sync in __arm_lpae_clear_pte().
>> - Merged both patches into this single patch by adding check for a
>>    NULL gather in __arm_lpae_unmap() itself.
>
> Yeah, that's cleaned up really nicely!
>
> Other than a nit that the subject ideally wants to be something more
> accurate like "iommu/io-pgtable-arm: Optimise non-coherent unmap" (sorry
> I forgot to mention that last time),
>
> Reviewed-by: Robin Murphy <robin.murphy@arm.com>
>
Thanks Robin. I will update new patch with change in subject and add
your Reviewed-by tag.

>> ---
>>   drivers/iommu/io-pgtable-arm.c | 31 +++++++++++++++++--------------
>>   1 file changed, 17 insertions(+), 14 deletions(-)
>>
>> diff --git a/drivers/iommu/io-pgtable-arm.c 
>> b/drivers/iommu/io-pgtable-arm.c
>> index f5d9fd1f45bf..6fecf3d9fe67 100644
>> --- a/drivers/iommu/io-pgtable-arm.c
>> +++ b/drivers/iommu/io-pgtable-arm.c
>> @@ -274,13 +274,13 @@ static void __arm_lpae_sync_pte(arm_lpae_iopte 
>> *ptep, int num_entries,
>>                                  sizeof(*ptep) * num_entries, 
>> DMA_TO_DEVICE);
>>   }
>>
>> -static void __arm_lpae_clear_pte(arm_lpae_iopte *ptep, struct 
>> io_pgtable_cfg *cfg)
>> +static void __arm_lpae_clear_pte(arm_lpae_iopte *ptep, struct 
>> io_pgtable_cfg *cfg, int num_entries)
>>   {
>> +     for (int i = 0; i < num_entries; i++)
>> +             ptep[i] = 0;
>>
>> -     *ptep = 0;
>> -
>> -     if (!cfg->coherent_walk)
>> -             __arm_lpae_sync_pte(ptep, 1, cfg);
>> +     if (!cfg->coherent_walk && num_entries)
>> +             __arm_lpae_sync_pte(ptep, num_entries, cfg);
>>   }
>>
>>   static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
>> @@ -654,26 +654,29 @@ static size_t __arm_lpae_unmap(struct 
>> arm_lpae_io_pgtable *data,
>>               max_entries = ARM_LPAE_PTES_PER_TABLE(data) - 
>> unmap_idx_start;
>>               num_entries = min_t(int, pgcount, max_entries);
>>
>> -             while (i < num_entries) {
>> -                     pte = READ_ONCE(*ptep);
>> +             /* Find and handle non-leaf entries */
>> +             for (i = 0; i < num_entries; i++) {
>> +                     pte = READ_ONCE(ptep[i]);
>>                       if (WARN_ON(!pte))
>>                               break;
>>
>> -                     __arm_lpae_clear_pte(ptep, &iop->cfg);
>> -
>>                       if (!iopte_leaf(pte, lvl, iop->fmt)) {
>> +                             __arm_lpae_clear_pte(&ptep[i], 
>> &iop->cfg, 1);
>> +
>>                               /* Also flush any partial walks */
>>                               io_pgtable_tlb_flush_walk(iop, iova + i 
>> * size, size,
>> ARM_LPAE_GRANULE(data));
>>                               __arm_lpae_free_pgtable(data, lvl + 1, 
>> iopte_deref(pte, data));
>> -                     } else if (!iommu_iotlb_gather_queued(gather)) {
>> -                             io_pgtable_tlb_add_page(iop, gather, 
>> iova + i * size, size);
>>                       }
>> -
>> -                     ptep++;
>> -                     i++;
>>               }
>>
>> +             /* Clear the remaining entries */
>> +             __arm_lpae_clear_pte(ptep, &iop->cfg, i);
>> +
>> +             if (gather && !iommu_iotlb_gather_queued(gather))
>> +                     for (int j = 0; j < i; j++)
>> +                             io_pgtable_tlb_add_page(iop, gather, 
>> iova + j * size, size);
>> +
>>               return i * size;
>>       } else if (iopte_leaf(pte, lvl, iop->fmt)) {
>>               /*
diff mbox series

Patch

diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index f5d9fd1f45bf..6fecf3d9fe67 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -274,13 +274,13 @@  static void __arm_lpae_sync_pte(arm_lpae_iopte *ptep, int num_entries,
 				   sizeof(*ptep) * num_entries, DMA_TO_DEVICE);
 }
 
-static void __arm_lpae_clear_pte(arm_lpae_iopte *ptep, struct io_pgtable_cfg *cfg)
+static void __arm_lpae_clear_pte(arm_lpae_iopte *ptep, struct io_pgtable_cfg *cfg, int num_entries)
 {
+	for (int i = 0; i < num_entries; i++)
+		ptep[i] = 0;
 
-	*ptep = 0;
-
-	if (!cfg->coherent_walk)
-		__arm_lpae_sync_pte(ptep, 1, cfg);
+	if (!cfg->coherent_walk && num_entries)
+		__arm_lpae_sync_pte(ptep, num_entries, cfg);
 }
 
 static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
@@ -654,26 +654,29 @@  static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
 		max_entries = ARM_LPAE_PTES_PER_TABLE(data) - unmap_idx_start;
 		num_entries = min_t(int, pgcount, max_entries);
 
-		while (i < num_entries) {
-			pte = READ_ONCE(*ptep);
+		/* Find and handle non-leaf entries */
+		for (i = 0; i < num_entries; i++) {
+			pte = READ_ONCE(ptep[i]);
 			if (WARN_ON(!pte))
 				break;
 
-			__arm_lpae_clear_pte(ptep, &iop->cfg);
-
 			if (!iopte_leaf(pte, lvl, iop->fmt)) {
+				__arm_lpae_clear_pte(&ptep[i], &iop->cfg, 1);
+
 				/* Also flush any partial walks */
 				io_pgtable_tlb_flush_walk(iop, iova + i * size, size,
 							  ARM_LPAE_GRANULE(data));
 				__arm_lpae_free_pgtable(data, lvl + 1, iopte_deref(pte, data));
-			} else if (!iommu_iotlb_gather_queued(gather)) {
-				io_pgtable_tlb_add_page(iop, gather, iova + i * size, size);
 			}
-
-			ptep++;
-			i++;
 		}
 
+		/* Clear the remaining entries */
+		__arm_lpae_clear_pte(ptep, &iop->cfg, i);
+
+		if (gather && !iommu_iotlb_gather_queued(gather))
+			for (int j = 0; j < i; j++)
+				io_pgtable_tlb_add_page(iop, gather, iova + j * size, size);
+
 		return i * size;
 	} else if (iopte_leaf(pte, lvl, iop->fmt)) {
 		/*