On 01/08/2024 4:34 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@xxxxxxxxxx>
---
Changes in V2:
- Updated the commit message to be imperative.
- Fixed ptep at incorrect index getting cleared for non-leaf entries.
---
drivers/iommu/io-pgtable-arm.c | 34 +++++++++++++++++++++-------------
1 file changed, 21 insertions(+), 13 deletions(-)
diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index f5d9fd1f45bf..32401948b980 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -274,13 +274,15 @@ 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)
{
+ int i;
You can make this a nice tidy loop-local declaration now.
- *ptep = 0;
+ for (i = 0; i < num_entries; i++)
+ ptep[i] = 0;
if (!cfg->coherent_walk)
- __arm_lpae_sync_pte(ptep, 1, cfg);
+ __arm_lpae_sync_pte(ptep, num_entries, cfg);
}
static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
@@ -635,9 +637,10 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
unsigned long iova, size_t size, size_t pgcount,
int lvl, arm_lpae_iopte *ptep)
{
+ bool gather_queued;
arm_lpae_iopte pte;
struct io_pgtable *iop = &data->iop;
- int i = 0, num_entries, max_entries, unmap_idx_start;
+ int i = 0, j = 0, num_entries, max_entries, unmap_idx_start;
Similarly there's no need to initialise j here, but I'd make it
loop-local anyway.
/* Something went horribly wrong and we ran out of page table */
if (WARN_ON(lvl == ARM_LPAE_MAX_LEVELS))
@@ -652,28 +655,33 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
/* If the size matches this level, we're in the right place */
if (size == ARM_LPAE_BLOCK_SIZE(lvl, data)) {
max_entries = ARM_LPAE_PTES_PER_TABLE(data) - unmap_idx_start;
+ gather_queued = iommu_iotlb_gather_queued(gather);
This is used exactly once, do we really need to introduce the variable?
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 */
+ if (i)
It seems a little non-obvious to optimise for one specific corner of
unexpected failures here. I'd hope a zero-sized dma_sync wouldn't blow
up in that case, but if you want to be safe then I'd cover it by
tweaking the condition in __arm_lpae_clear_pte() to "if
(!cfg->coherent_walk && num_entries)".
Thanks,
Robin.
+ __arm_lpae_clear_pte(ptep, &iop->cfg, i);
+
+ if (!gather_queued)
+ for (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)) {
/*
