[Qemu-devel] [RFC v6 09/14] softmmu: Add history of excl accesses

[Alvise Rigo]

Add a circular buffer to store the hw addresses used in the last
EXCLUSIVE_HISTORY_LEN exclusive accesses.

When an address is pop'ed from the buffer, its page will be set as not
exclusive. In this way, we avoid:
- frequent set/unset of a page (causing frequent flushes as well)
- the possibility to forget the EXCL bit set.

Suggested-by: Jani Kokkonen <address@hidden>
Suggested-by: Claudio Fontana <address@hidden>
Signed-off-by: Alvise Rigo <address@hidden>
---
 cputlb.c                | 32 ++++++++++++++++++++++----------
 include/qom/cpu.h       |  3 +++
 softmmu_llsc_template.h |  2 ++
 3 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/cputlb.c b/cputlb.c
index 70b6404..372877e 100644
--- a/cputlb.c
+++ b/cputlb.c
@@ -394,16 +394,6 @@ void tlb_set_page_with_attrs(CPUState *cpu, target_ulong 
vaddr,
     env->tlb_v_table[mmu_idx][vidx] = *te;
     env->iotlb_v[mmu_idx][vidx] = env->iotlb[mmu_idx][index];
 
-    if (unlikely(!(te->addr_write & TLB_MMIO) && (te->addr_write & TLB_EXCL))) 
{
-        /* We are removing an exclusive entry, set the page to dirty. This
-         * is not be necessary if the vCPU has performed both SC and LL. */
-        hwaddr hw_addr = (env->iotlb[mmu_idx][index].addr & TARGET_PAGE_MASK) +
-                                          (te->addr_write & TARGET_PAGE_MASK);
-        if (!cpu->ll_sc_context) {
-            cpu_physical_memory_unset_excl(hw_addr, cpu->cpu_index);
-        }
-    }
-
     /* refill the tlb */
     env->iotlb[mmu_idx][index].addr = iotlb - vaddr;
     env->iotlb[mmu_idx][index].attrs = attrs;
@@ -507,6 +497,28 @@ static inline void lookup_and_reset_cpus_ll_addr(hwaddr 
addr, hwaddr size)
     }
 }
 
+static inline void excl_history_put_addr(CPUState *cpu, hwaddr addr)
+{
+    /* Avoid some overhead if the address we are about to put is equal to
+     * the last one */
+    if (cpu->excl_protected_addr[cpu->excl_protected_last] !=
+                                    (addr & TARGET_PAGE_MASK)) {
+        cpu->excl_protected_last = (cpu->excl_protected_last + 1) %
+                                            EXCLUSIVE_HISTORY_LEN;
+        /* Unset EXCL bit of the oldest entry */
+        if (cpu->excl_protected_addr[cpu->excl_protected_last] !=
+                                            EXCLUSIVE_RESET_ADDR) {
+            cpu_physical_memory_unset_excl(
+                cpu->excl_protected_addr[cpu->excl_protected_last],
+                cpu->cpu_index);
+        }
+
+        /* Add a new address, overwriting the oldest one */
+        cpu->excl_protected_addr[cpu->excl_protected_last] =
+                                            addr & TARGET_PAGE_MASK;
+    }
+}
+
 #define MMUSUFFIX _mmu
 
 /* Generates LoadLink/StoreConditional helpers in softmmu_template.h */
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 9e409ce..5f65ebf 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -217,6 +217,7 @@ struct kvm_run;
 
 /* Atomic insn translation TLB support. */
 #define EXCLUSIVE_RESET_ADDR ULLONG_MAX
+#define EXCLUSIVE_HISTORY_LEN 8
 
 /**
  * CPUState:
@@ -343,6 +344,8 @@ struct CPUState {
      * The address is set to EXCLUSIVE_RESET_ADDR if the vCPU is not.
      * in the middle of a LL/SC. */
     struct Range excl_protected_range;
+    hwaddr excl_protected_addr[EXCLUSIVE_HISTORY_LEN];
+    int excl_protected_last;
     /* Used to carry the SC result but also to flag a normal (legacy)
      * store access made by a stcond (see softmmu_template.h). */
     int excl_succeeded;
diff --git a/softmmu_llsc_template.h b/softmmu_llsc_template.h
index 586bb2e..becb90b 100644
--- a/softmmu_llsc_template.h
+++ b/softmmu_llsc_template.h
@@ -72,6 +72,7 @@ WORD_TYPE helper_ldlink_name(CPUArchState *env, target_ulong 
addr,
     hw_addr = (env->iotlb[mmu_idx][index].addr & TARGET_PAGE_MASK) + addr;
 
     cpu_physical_memory_set_excl(hw_addr, this->cpu_index);
+    excl_history_put_addr(this, hw_addr);
     /* If all the vCPUs have the EXCL bit set for this page there is no need
      * to request any flush. */
     if (cpu_physical_memory_not_excl(hw_addr, smp_cpus)) {
@@ -80,6 +81,7 @@ WORD_TYPE helper_ldlink_name(CPUArchState *env, target_ulong 
addr,
                 if (cpu_physical_memory_not_excl(hw_addr, cpu->cpu_index)) {
                     cpu_physical_memory_set_excl(hw_addr, cpu->cpu_index);
                     tlb_flush(cpu, 1);
+                    excl_history_put_addr(cpu, hw_addr);
                 }
             }
         }
-- 
2.6.4