| Message ID | 20240801033432.106837-1-amhetre@nvidia.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [V2,1/2] iommu: Optimize IOMMU UnMap | expand |
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@nvidia.com> > --- > 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)) { > /*
On 8/1/2024 9:53 PM, Robin Murphy wrote: > External email: Use caution opening links or attachments > > > 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@nvidia.com> >> --- >> 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. > Sure, will update this in new version. >> - *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. > Ack, I will make j loop-local. >> /* 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? > Ack, I will remove the unnecessary 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. > Yes, makes sense to cover this in __arm_lpae_clear_pte(). I will update this in V3. >> + __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)) { >> /*
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; - *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; /* 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); 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) + __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)) { /*
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. --- drivers/iommu/io-pgtable-arm.c | 34 +++++++++++++++++++++------------- 1 file changed, 21 insertions(+), 13 deletions(-)