accel/tcg: increase default code gen buffer size for 64 bit

While 32mb is certainly usable a full system boot ends up flushing the
codegen buffer nearly 100 times. Increase the default on 64 bit hosts
to take advantage of all that spare memory. After this change I can
boot my tests system without any TB flushes.

As we usually run more CONFIG_USER binaries at a time in typical usage
we aren't quite as profligate for user-mode code generation usage. We
also bring the static code gen defies to the same place to keep all
the reasoning in the comments together.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Reviewed-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Message-Id: <20200228192415.19867-5-alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

accel/tcg/translate-all.c

@@ -892,15 +892,6 @@ static void page_lock_pair(PageDesc **ret_p1, tb_page_addr_t phys1,
     }
 }
 
-#if defined(CONFIG_USER_ONLY) && TCG_TARGET_REG_BITS == 32
-/*
- * For user mode on smaller 32 bit systems we may run into trouble
- * allocating big chunks of data in the right place. On these systems
- * we utilise a static code generation buffer directly in the binary.
- */
-#define USE_STATIC_CODE_GEN_BUFFER
-#endif
-
 /* Minimum size of the code gen buffer.  This number is randomly chosen,
    but not so small that we can't have a fair number of TB's live.  */
 #define MIN_CODE_GEN_BUFFER_SIZE     (1 * MiB)
@@ -929,7 +920,33 @@ static void page_lock_pair(PageDesc **ret_p1, tb_page_addr_t phys1,
 # define MAX_CODE_GEN_BUFFER_SIZE  ((size_t)-1)
 #endif
 
+#if TCG_TARGET_REG_BITS == 32
 #define DEFAULT_CODE_GEN_BUFFER_SIZE_1 (32 * MiB)
+#ifdef CONFIG_USER_ONLY
+/*
+ * For user mode on smaller 32 bit systems we may run into trouble
+ * allocating big chunks of data in the right place. On these systems
+ * we utilise a static code generation buffer directly in the binary.
+ */
+#define USE_STATIC_CODE_GEN_BUFFER
+#endif
+#else /* TCG_TARGET_REG_BITS == 64 */
+#ifdef CONFIG_USER_ONLY
+/*
+ * As user-mode emulation typically means running multiple instances
+ * of the translator don't go too nuts with our default code gen
+ * buffer lest we make things too hard for the OS.
+ */
+#define DEFAULT_CODE_GEN_BUFFER_SIZE_1 (128 * MiB)
+#else
+/*
+ * We expect most system emulation to run one or two guests per host.
+ * Users running large scale system emulation may want to tweak their
+ * runtime setup via the tb-size control on the command line.
+ */
+#define DEFAULT_CODE_GEN_BUFFER_SIZE_1 (1 * GiB)
+#endif
+#endif
 
 #define DEFAULT_CODE_GEN_BUFFER_SIZE \
   (DEFAULT_CODE_GEN_BUFFER_SIZE_1 < MAX_CODE_GEN_BUFFER_SIZE \