[Qemu-devel] [RFC v8 08/14] 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).

Suggested-by: Jani Kokkonen <address@hidden>
Suggested-by: Claudio Fontana <address@hidden>
Signed-off-by: Alvise Rigo <address@hidden>
---
 cputlb.c                | 21 +++++++++++++++++++++
 exec.c                  | 19 +++++++++++++++++++
 include/qom/cpu.h       |  8 ++++++++
 softmmu_llsc_template.h |  1 +
 vl.c                    |  3 +++
 5 files changed, 52 insertions(+)

diff --git a/cputlb.c b/cputlb.c
index 58d6f03..02b0d14 100644
--- a/cputlb.c
+++ b/cputlb.c
@@ -475,6 +475,27 @@ tb_page_addr_t get_page_addr_code(CPUArchState *env1, 
target_ulong addr)
     return qemu_ram_addr_from_host_nofail(p);
 }
 
+/* Keep a circular array with the last excl_history.length addresses used for
+ * exclusive accesses. The exiting addresses are marked as non-exclusive. */
+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 cefee1b..3c54b92 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 014851e..de144f6 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -232,7 +232,15 @@ 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 ca2ac95..1e24fec 100644
--- a/softmmu_llsc_template.h
+++ b/softmmu_llsc_template.h
@@ -77,6 +77,7 @@ WORD_TYPE helper_ldlink_name(CPUArchState *env, target_ulong 
addr,
             CPUState *cpu;
 
             cpu_physical_memory_set_excl(hw_addr);
+            excl_history_put_addr(hw_addr);
             CPU_FOREACH(cpu) {
                 if (this_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);
     }
-- 
2.8.0