1 files changed, 137 insertions, 9 deletions

diff --git a/tcg/tcg.c b/tcg/tcg.c
index 3de5f7cf97..5574317736 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -58,6 +58,7 @@
 
 #include "elf.h"
 #include "exec/log.h"
+#include "sysemu/sysemu.h"
 
 /* Forward declarations for functions declared in tcg-target.inc.c and
    used here. */
@@ -353,25 +354,87 @@ static inline bool tcg_region_initial_alloc__locked(TCGContext *s)
 /* Call from a safe-work context */
 void tcg_region_reset_all(void)
 {
+    unsigned int n_ctxs = atomic_read(&n_tcg_ctxs);
     unsigned int i;
 
     qemu_mutex_lock(&region.lock);
     region.current = 0;
     region.agg_size_full = 0;
 
-    for (i = 0; i < n_tcg_ctxs; i++) {
-        bool err = tcg_region_initial_alloc__locked(tcg_ctxs[i]);
+    for (i = 0; i < n_ctxs; i++) {
+        TCGContext *s = atomic_read(&tcg_ctxs[i]);
+        bool err = tcg_region_initial_alloc__locked(s);
 
         g_assert(!err);
     }
     qemu_mutex_unlock(&region.lock);
 }
 
+#ifdef CONFIG_USER_ONLY
+static size_t tcg_n_regions(void)
+{
+    return 1;
+}
+#else
+/*
+ * It is likely that some vCPUs will translate more code than others, so we
+ * first try to set more regions than max_cpus, with those regions being of
+ * reasonable size. If that's not possible we make do by evenly dividing
+ * the code_gen_buffer among the vCPUs.
+ */
+static size_t tcg_n_regions(void)
+{
+    size_t i;
+
+    /* Use a single region if all we have is one vCPU thread */
+    if (max_cpus == 1 || !qemu_tcg_mttcg_enabled()) {
+        return 1;
+    }
+
+    /* Try to have more regions than max_cpus, with each region being >= 2 MB */
+    for (i = 8; i > 0; i--) {
+        size_t regions_per_thread = i;
+        size_t region_size;
+
+        region_size = tcg_init_ctx.code_gen_buffer_size;
+        region_size /= max_cpus * regions_per_thread;
+
+        if (region_size >= 2 * 1024u * 1024) {
+            return max_cpus * regions_per_thread;
+        }
+    }
+    /* If we can't, then just allocate one region per vCPU thread */
+    return max_cpus;
+}
+#endif
+
 /*
  * Initializes region partitioning.
  *
  * Called at init time from the parent thread (i.e. the one calling
  * tcg_context_init), after the target's TCG globals have been set.
+ *
+ * Region partitioning works by splitting code_gen_buffer into separate regions,
+ * and then assigning regions to TCG threads so that the threads can translate
+ * code in parallel without synchronization.
+ *
+ * In softmmu the number of TCG threads is bounded by max_cpus, so we use at
+ * least max_cpus regions in MTTCG. In !MTTCG we use a single region.
+ * Note that the TCG options from the command-line (i.e. -accel accel=tcg,[...])
+ * must have been parsed before calling this function, since it calls
+ * qemu_tcg_mttcg_enabled().
+ *
+ * In user-mode we use a single region.  Having multiple regions in user-mode
+ * is not supported, because the number of vCPU threads (recall that each thread
+ * spawned by the guest corresponds to a vCPU thread) is only bounded by the
+ * OS, and usually this number is huge (tens of thousands is not uncommon).
+ * Thus, given this large bound on the number of vCPU threads and the fact
+ * that code_gen_buffer is allocated at compile-time, we cannot guarantee
+ * that the availability of at least one region per vCPU thread.
+ *
+ * However, this user-mode limitation is unlikely to be a significant problem
+ * in practice. Multi-threaded guests share most if not all of their translated
+ * code, which makes parallel code generation less appealing than in softmmu.
  */
 void tcg_region_init(void)
 {
@@ -383,8 +446,7 @@ void tcg_region_init(void)
     size_t n_regions;
     size_t i;
 
-    /* We do not yet support multiple TCG contexts, so use one region for now */
-    n_regions = 1;
+    n_regions = tcg_n_regions();
 
     /* The first region will be 'aligned - buf' bytes larger than the others */
     aligned = QEMU_ALIGN_PTR_UP(buf, page_size);
@@ -422,13 +484,66 @@ void tcg_region_init(void)
         g_assert(!rc);
     }
 
-    /* We do not yet support multiple TCG contexts so allocate the region now */
+    /* In user-mode we support only one ctx, so do the initial allocation now */
+#ifdef CONFIG_USER_ONLY
     {
         bool err = tcg_region_initial_alloc__locked(tcg_ctx);
 
         g_assert(!err);
     }
+#endif
+}
+
+/*
+ * All TCG threads except the parent (i.e. the one that called tcg_context_init
+ * and registered the target's TCG globals) must register with this function
+ * before initiating translation.
+ *
+ * In user-mode we just point tcg_ctx to tcg_init_ctx. See the documentation
+ * of tcg_region_init() for the reasoning behind this.
+ *
+ * In softmmu each caller registers its context in tcg_ctxs[]. Note that in
+ * softmmu tcg_ctxs[] does not track tcg_ctx_init, since the initial context
+ * is not used anymore for translation once this function is called.
+ *
+ * Not tracking tcg_init_ctx in tcg_ctxs[] in softmmu keeps code that iterates
+ * over the array (e.g. tcg_code_size() the same for both softmmu and user-mode.
+ */
+#ifdef CONFIG_USER_ONLY
+void tcg_register_thread(void)
+{
+    tcg_ctx = &tcg_init_ctx;
+}
+#else
+void tcg_register_thread(void)
+{
+    TCGContext *s = g_malloc(sizeof(*s));
+    unsigned int i, n;
+    bool err;
+
+    *s = tcg_init_ctx;
+
+    /* Relink mem_base.  */
+    for (i = 0, n = tcg_init_ctx.nb_globals; i < n; ++i) {
+        if (tcg_init_ctx.temps[i].mem_base) {
+            ptrdiff_t b = tcg_init_ctx.temps[i].mem_base - tcg_init_ctx.temps;
+            tcg_debug_assert(b >= 0 && b < n);
+            s->temps[i].mem_base = &s->temps[b];
+        }
+    }
+
+    /* Claim an entry in tcg_ctxs */
+    n = atomic_fetch_inc(&n_tcg_ctxs);
+    g_assert(n < max_cpus);
+    atomic_set(&tcg_ctxs[n], s);
+
+    tcg_ctx = s;
+    qemu_mutex_lock(&region.lock);
+    err = tcg_region_initial_alloc__locked(tcg_ctx);
+    g_assert(!err);
+    qemu_mutex_unlock(&region.lock);
 }
+#endif /* !CONFIG_USER_ONLY */
 
 /*
  * Returns the size (in bytes) of all translated code (i.e. from all regions)
@@ -439,13 +554,14 @@ void tcg_region_init(void)
  */
 size_t tcg_code_size(void)
 {
+    unsigned int n_ctxs = atomic_read(&n_tcg_ctxs);
     unsigned int i;
     size_t total;
 
     qemu_mutex_lock(&region.lock);
     total = region.agg_size_full;
-    for (i = 0; i < n_tcg_ctxs; i++) {
-        const TCGContext *s = tcg_ctxs[i];
+    for (i = 0; i < n_ctxs; i++) {
+        const TCGContext *s = atomic_read(&tcg_ctxs[i]);
         size_t size;
 
         size = atomic_read(&s->code_gen_ptr) - s->code_gen_buffer;
@@ -601,8 +717,18 @@ void tcg_context_init(TCGContext *s)
     }
 
     tcg_ctx = s;
+    /*
+     * In user-mode we simply share the init context among threads, since we
+     * use a single region. See the documentation tcg_region_init() for the
+     * reasoning behind this.
+     * In softmmu we will have at most max_cpus TCG threads.
+     */
+#ifdef CONFIG_USER_ONLY
     tcg_ctxs = &tcg_ctx;
     n_tcg_ctxs = 1;
+#else
+    tcg_ctxs = g_new(TCGContext *, max_cpus);
+#endif
 }
 
 /*
@@ -2951,10 +3077,12 @@ static void tcg_reg_alloc_call(TCGContext *s, TCGOp *op)
 static inline
 void tcg_profile_snapshot(TCGProfile *prof, bool counters, bool table)
 {
+    unsigned int n_ctxs = atomic_read(&n_tcg_ctxs);
     unsigned int i;
 
-    for (i = 0; i < n_tcg_ctxs; i++) {
-        const TCGProfile *orig = &tcg_ctxs[i]->prof;
+    for (i = 0; i < n_ctxs; i++) {
+        TCGContext *s = atomic_read(&tcg_ctxs[i]);
+        const TCGProfile *orig = &s->prof;
 
         if (counters) {
             PROF_ADD(prof, orig, tb_count1);