[Qemu-devel] [RFC v7 13/16] 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                | 29 +++++++++++++++++++----------
 exec.c                  | 19 +++++++++++++++++++
 include/qom/cpu.h       |  8 ++++++++
 softmmu_llsc_template.h |  1 +
 vl.c                    |  3 +++
 5 files changed, 50 insertions(+), 10 deletions(-)

diff --git a/cputlb.c b/cputlb.c
index 06ce2da..f3c4d97 100644
--- a/cputlb.c
+++ b/cputlb.c
@@ -395,16 +395,6 @@ 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);
-        }
-    }
-
     /* refill the tlb */
     env->iotlb[mmu_idx][index].addr = iotlb - vaddr;
     env->iotlb[mmu_idx][index].attrs = attrs;
@@ -517,6 +507,25 @@ static inline bool lookup_and_reset_cpus_ll_addr(hwaddr 
addr, hwaddr size)
     return ret;
 }
 
+extern CPUExclusiveHistory excl_history;
+static inline void excl_history_put_addr(hwaddr addr)
+{
+    hwaddr last;
+
+    /* Calculate the index of the next exclusive address */
+    excl_history.last_idx = (excl_history.last_idx + 1) % excl_history.length;
+
+    last = excl_history.c_array[excl_history.last_idx];
+
+    /* Unset EXCL bit of the oldest entry */
+    if (last != EXCLUSIVE_RESET_ADDR) {
+        cpu_physical_memory_unset_excl(last);
+    }
+
+    /* Add a new address, overwriting the oldest one */
+    excl_history.c_array[excl_history.last_idx] = addr & TARGET_PAGE_MASK;
+}
+
 #define MMUSUFFIX _mmu
 
 /* Generates LoadLink/StoreConditional helpers in softmmu_template.h */
diff --git a/exec.c b/exec.c
index 51f366d..2e123f1 100644
--- a/exec.c
+++ b/exec.c
@@ -177,6 +177,25 @@ struct CPUAddressSpace {
     MemoryListener tcg_as_listener;
 };
 
+/* Exclusive memory support */
+CPUExclusiveHistory excl_history;
+void cpu_exclusive_history_init(void)
+{
+    /* Initialize exclusive history for atomic instruction handling. */
+    if (tcg_enabled()) {
+        g_assert(EXCLUSIVE_HISTORY_CPU_LEN * max_cpus <= UINT16_MAX);
+        excl_history.length = EXCLUSIVE_HISTORY_CPU_LEN * max_cpus;
+        excl_history.c_array = g_malloc(excl_history.length * sizeof(hwaddr));
+        memset(excl_history.c_array, -1, excl_history.length * sizeof(hwaddr));
+    }
+}
+
+void cpu_exclusive_history_free(void)
+{
+    if (tcg_enabled()) {
+        g_free(excl_history.c_array);
+    }
+}
 #endif
 
 #if !defined(CONFIG_USER_ONLY)
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 6f6c1c0..0452fd0 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -227,7 +227,15 @@ struct kvm_run;
 #define TB_JMP_CACHE_SIZE (1 << TB_JMP_CACHE_BITS)
 
 /* Atomic insn translation TLB support. */
+typedef struct CPUExclusiveHistory {
+    uint16_t last_idx;           /* index of last insertion */
+    uint16_t length;             /* history's length, it depends on smp_cpus */
+    hwaddr *c_array;             /* history's circular array */
+} CPUExclusiveHistory;
 #define EXCLUSIVE_RESET_ADDR ULLONG_MAX
+#define EXCLUSIVE_HISTORY_CPU_LEN 256
+void cpu_exclusive_history_init(void);
+void cpu_exclusive_history_free(void);
 
 /**
  * CPUState:
diff --git a/softmmu_llsc_template.h b/softmmu_llsc_template.h
index b4712ba..b4e7f9d 100644
--- a/softmmu_llsc_template.h
+++ b/softmmu_llsc_template.h
@@ -75,6 +75,7 @@ WORD_TYPE helper_ldlink_name(CPUArchState *env, target_ulong 
addr,
          * to request any flush. */
         if (!cpu_physical_memory_is_excl(hw_addr)) {
             cpu_physical_memory_set_excl(hw_addr);
+            excl_history_put_addr(hw_addr);
             CPU_FOREACH(cpu) {
                 if (current_cpu != cpu) {
                     tlb_flush(cpu, 1);
diff --git a/vl.c b/vl.c
index f043009..b22d99b 100644
--- a/vl.c
+++ b/vl.c
@@ -547,6 +547,7 @@ static void res_free(void)
 {
     g_free(boot_splash_filedata);
     boot_splash_filedata = NULL;
+    cpu_exclusive_history_free();
 }
 
 static int default_driver_check(void *opaque, QemuOpts *opts, Error **errp)
@@ -4322,6 +4323,8 @@ int main(int argc, char **argv, char **envp)
 
     configure_accelerator(current_machine);
 
+    cpu_exclusive_history_init();
+
     if (qtest_chrdev) {
         qtest_init(qtest_chrdev, qtest_log, &error_fatal);
     }
-- 
2.7.0