tests/plugin: add a hotblocks plugin

This is a simple plugin to track which translation blocks are call
most often. As we don't have a view of the internals of TCG we can
only work by the address of the start of the block so we also need to
tracks how often the address is translated.

As there will be multiple blocks starting at the same address. We can
try and work around this by futzing the value to feed to the hash with
the insn count.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

tests/plugin/Makefile

@@ -10,6 +10,7 @@ NAMES += bb
 NAMES += empty
 NAMES += insn
 NAMES += mem
+NAMES += hotblocks
 
 SONAMES := $(addsuffix .so,$(addprefix lib,$(NAMES)))
 

tests/plugin/hotblocks.c

@@ -0,0 +1,143 @@
+/*
+ * Copyright (C) 2019, Alex Bennée <alex.bennee@linaro.org>
+ *
+ * License: GNU GPL, version 2 or later.
+ *   See the COPYING file in the top-level directory.
+ */
+#include <inttypes.h>
+#include <assert.h>
+#include <stdlib.h>
+#include <inttypes.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <glib.h>
+
+#include <qemu-plugin.h>
+
+static bool do_inline;
+
+/* Plugins need to take care of their own locking */
+static GMutex lock;
+static GHashTable *hotblocks;
+static guint64 limit = 20;
+
+/*
+ * Counting Structure
+ *
+ * The internals of the TCG are not exposed to plugins so we can only
+ * get the starting PC for each block. We cheat this slightly by
+ * xor'ing the number of instructions to the hash to help
+ * differentiate.
+ */
+typedef struct {
+    uint64_t start_addr;
+    uint64_t exec_count;
+    int      trans_count;
+    unsigned long insns;
+} ExecCount;
+
+static gint cmp_exec_count(gconstpointer a, gconstpointer b)
+{
+    ExecCount *ea = (ExecCount *) a;
+    ExecCount *eb = (ExecCount *) b;
+    return ea->exec_count > eb->exec_count ? -1 : 1;
+}
+
+static void plugin_exit(qemu_plugin_id_t id, void *p)
+{
+    g_autoptr(GString) report = g_string_new("collected ");
+    GList *counts, *it;
+    int i;
+
+    g_mutex_lock(&lock);
+    g_string_append_printf(report, "%d entries in the hash table\n",
+                           g_hash_table_size(hotblocks));
+    counts = g_hash_table_get_values(hotblocks);
+    it = g_list_sort(counts, cmp_exec_count);
+
+    if (it) {
+        g_string_append_printf(report, "pc, tcount, icount, ecount\n");
+
+        for (i = 0; i < limit && it->next; i++, it = it->next) {
+            ExecCount *rec = (ExecCount *) it->data;
+            g_string_append_printf(report, "%#016"PRIx64", %d, %ld, %"PRId64"\n",
+                                   rec->start_addr, rec->trans_count,
+                                   rec->insns, rec->exec_count);
+        }
+
+        g_list_free(it);
+        g_mutex_unlock(&lock);
+    }
+
+    qemu_plugin_outs(report->str);
+}
+
+static void plugin_init(void)
+{
+    hotblocks = g_hash_table_new(NULL, g_direct_equal);
+}
+
+static void vcpu_tb_exec(unsigned int cpu_index, void *udata)
+{
+    ExecCount *cnt;
+    uint64_t hash = (uint64_t) udata;
+
+    g_mutex_lock(&lock);
+    cnt = (ExecCount *) g_hash_table_lookup(hotblocks, (gconstpointer) hash);
+    /* should always succeed */
+    g_assert(cnt);
+    cnt->exec_count++;
+    g_mutex_unlock(&lock);
+}
+
+/*
+ * When do_inline we ask the plugin to increment the counter for us.
+ * Otherwise a helper is inserted which calls the vcpu_tb_exec
+ * callback.
+ */
+static void vcpu_tb_trans(qemu_plugin_id_t id, struct qemu_plugin_tb *tb)
+{
+    ExecCount *cnt;
+    uint64_t pc = qemu_plugin_tb_vaddr(tb);
+    unsigned long insns = qemu_plugin_tb_n_insns(tb);
+    uint64_t hash = pc ^ insns;
+
+    g_mutex_lock(&lock);
+    cnt = (ExecCount *) g_hash_table_lookup(hotblocks, (gconstpointer) hash);
+    if (cnt) {
+        cnt->trans_count++;
+    } else {
+        cnt = g_new0(ExecCount, 1);
+        cnt->start_addr = pc;
+        cnt->trans_count = 1;
+        cnt->insns = insns;
+        g_hash_table_insert(hotblocks, (gpointer) hash, (gpointer) cnt);
+    }
+
+    g_mutex_unlock(&lock);
+
+    if (do_inline) {
+        qemu_plugin_register_vcpu_tb_exec_inline(tb, QEMU_PLUGIN_INLINE_ADD_U64,
+                                                 &cnt->exec_count, 1);
+    } else {
+        qemu_plugin_register_vcpu_tb_exec_cb(tb, vcpu_tb_exec,
+                                             QEMU_PLUGIN_CB_NO_REGS,
+                                             (void *)hash);
+    }
+}
+
+QEMU_PLUGIN_EXPORT
+int qemu_plugin_install(qemu_plugin_id_t id, const qemu_info_t *info,
+                        int argc, char **argv)
+{
+    if (argc && strcmp(argv[0], "inline") == 0) {
+        do_inline = true;
+    }
+
+    plugin_init();
+
+    qemu_plugin_register_vcpu_tb_trans_cb(id, vcpu_tb_trans);
+    qemu_plugin_register_atexit_cb(id, plugin_exit, NULL);
+    return 0;
+}