[Libguestfs] [PATCH libnbd] lib: Use GCC hints to move debug and error handling code out of hot paths.

--- generator/generator | 6 +++--- lib/crypto.c | 2 +- lib/internal.h | 14 +++++++++++++- 3 files changed, 17 insertions(+), 5 deletions(-) diff --git a/generator/generator b/generator/generator index c2ff0db..eb3408d 100755 --- a/generator/generator +++ b/generator/generator @@ -4512,7 +4512,7 @@ let generate_lib_api_c () = let value = match errcode with | Some value -> value | None -> assert false in - pr " if (!%s_in_permitted_state (h)) {\n" name; + pr " if (unlikely (!%s_in_permitted_state (h))) {\n" name; pr " ret = %s;\n" value; pr " goto out;\n"; pr " }\n"; @@ -4525,7 +4525,7 @@ let generate_lib_api_c () = | Some value -> value | None -> assert false in let mask = List.fold_left (lor) 0 (List.map snd flags) in - pr " if ((%s & ~%d) != 0) {\n" n mask; + pr " if (unlikely ((%s & ~%d) != 0)) {\n" n mask; pr " set_error (EINVAL, \"%%s: invalid value for flag: %%d\",\n"; pr " \"%s\", %s);\n" n n; pr " ret = %s;\n" value; @@ -4658,7 +4658,7 @@ let generate_lib_api_c () = pr ");\n" (* Print the trace when we leave a call with debugging enabled. *) and print_trace_leave ret = - pr " if (h->debug) {\n"; + pr " if_debug (h) {\n"; let errcode = errcode_of_ret ret in (match errcode with | Some r -> diff --git a/lib/crypto.c b/lib/crypto.c index 07d06c0..8d86911 100644 --- a/lib/crypto.c +++ b/lib/crypto.c @@ -676,7 +676,7 @@ nbd_internal_crypto_handshake (struct nbd_handle *h) void nbd_internal_crypto_debug_tls_enabled (struct nbd_handle *h) { - if (h->debug) { + if_debug (h) { const gnutls_session_t session = h->sock->u.tls.session; const gnutls_cipher_algorithm_t cipher = gnutls_cipher_get (session); const gnutls_kx_algorithm_t kx = gnutls_kx_get (session); diff --git a/lib/internal.h b/lib/internal.h index 50c0a9b..894e437 100644 --- a/lib/internal.h +++ b/lib/internal.h @@ -40,6 +40,18 @@ #include "states.h" #include "unlocked.h" +/* Define unlikely macro, but only for GCC. These are used to move + * debug and error handling code out of hot paths, making the hot path + * into common functions use less instruction cache. + */ +#if defined(__GNUC__) +#define unlikely(x) __builtin_expect (!!(x), 0) +#define if_debug(h) if (unlikely ((h)->debug)) +#else +#define unlikely(x) (x) +#define if_debug(h) if ((h)->debug) +#endif + /* MSG_MORE is an optimization. If not present, ignore it. */ #ifndef MSG_MORE #define MSG_MORE 0 @@ -329,7 +341,7 @@ extern void nbd_internal_crypto_debug_tls_enabled (struct nbd_handle *); extern void nbd_internal_debug (struct nbd_handle *h, const char *fs, ...); #define debug(h, fs, ...) \ do { \ - if ((h)->debug) \ + if_debug ((h)) \ nbd_internal_debug ((h), (fs), ##__VA_ARGS__); \ } while (0) -- 2.23.0