[PATCH 2/3] s390x/pci: coalesce unmap operations

[Matthew Rosato <mjrosato@linux.ibm.com>]

Currently, each unmapped page is handled as an individual iommu
region notification.  Attempt to group contiguous unmap operations
into fewer notifications to reduce overhead.

Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
---
 hw/s390x/s390-pci-inst.c | 51 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/hw/s390x/s390-pci-inst.c b/hw/s390x/s390-pci-inst.c
index 7cc4bcf850..66e764f901 100644
--- a/hw/s390x/s390-pci-inst.c
+++ b/hw/s390x/s390-pci-inst.c
@@ -640,6 +640,8 @@ static uint32_t s390_pci_update_iotlb(S390PCIIOMMU *iommu,
         }
         g_hash_table_remove(iommu->iotlb, &entry->iova);
         inc_dma_avail(iommu);
+        /* Don't notify the iommu yet, maybe we can bundle contiguous unmaps */
+        goto out;
     } else {
         if (cache) {
             if (cache->perm == entry->perm &&
@@ -663,15 +665,44 @@ static uint32_t s390_pci_update_iotlb(S390PCIIOMMU *iommu,
         dec_dma_avail(iommu);
     }
 
+    /*
+     * All associated iotlb entries have already been cleared, trigger the
+     * unmaps.
+     */
     memory_region_notify_iommu(&iommu->iommu_mr, 0, event);
 
 out:
     return iommu->dma_limit ? iommu->dma_limit->avail : 1;
 }
 
+static void s390_pci_batch_unmap(S390PCIIOMMU *iommu, uint64_t iova,
+                                 uint64_t len)
+{
+    uint64_t remain = len, start = iova, end = start + len - 1, mask, size;
+    IOMMUTLBEvent event = {
+        .type = IOMMU_NOTIFIER_UNMAP,
+        .entry = {
+            .target_as = &address_space_memory,
+            .translated_addr = 0,
+            .perm = IOMMU_NONE,
+        },
+    };
+
+    while (remain >= TARGET_PAGE_SIZE) {
+        mask = dma_aligned_pow2_mask(start, end, 64);
+        size = mask + 1;
+        event.entry.iova = start;
+        event.entry.addr_mask = mask;
+        memory_region_notify_iommu(&iommu->iommu_mr, 0, event);
+        start += size;
+        remain -= size;
+    }
+}
+
 int rpcit_service_call(S390CPU *cpu, uint8_t r1, uint8_t r2, uintptr_t ra)
 {
     CPUS390XState *env = &cpu->env;
+    uint64_t iova, coalesce = 0;
     uint32_t fh;
     uint16_t error = 0;
     S390PCIBusDevice *pbdev;
@@ -742,6 +773,21 @@ int rpcit_service_call(S390CPU *cpu, uint8_t r1, uint8_t r2, uintptr_t ra)
             break;
         }
 
+        /*
+         * If this is an unmap of a PTE, let's try to coalesce multiple unmaps
+         * into as few notifier events as possible.
+         */
+        if (entry.perm == IOMMU_NONE && entry.len == TARGET_PAGE_SIZE) {
+            if (coalesce == 0) {
+                iova = entry.iova;
+            }
+            coalesce += entry.len;
+        } else if (coalesce > 0) {
+            /* Unleash the coalesced unmap before processing a new map */
+            s390_pci_batch_unmap(iommu, iova, coalesce);
+            coalesce = 0;
+        }
+
         start += entry.len;
         while (entry.iova < start && entry.iova < end) {
             if (dma_avail > 0 || entry.perm == IOMMU_NONE) {
@@ -759,6 +805,11 @@ int rpcit_service_call(S390CPU *cpu, uint8_t r1, uint8_t r2, uintptr_t ra)
             }
         }
     }
+    if (coalesce) {
+            /* Unleash the coalesced unmap before finishing rpcit */
+            s390_pci_batch_unmap(iommu, iova, coalesce);
+            coalesce = 0;
+    }
     if (again && dma_avail > 0)
         goto retry;
 err:
-- 
2.37.3