dlt-system: Avoid expensive getpid() syscalls

Since glibc 2.25, getpid() no longer caches the PID, instead performing a full syscall every time. This means we're performing a full syscall roundtrip for *every* *single* *log* *message* on the system. This patch caches the result of getpid() when appropriate, avoiding unnessicary syscalls. Signed-off-by: Aleix Pol Gonzalez <[email protected]>
COVESA · Jan 8, 2025 · 34d8272 · 34d8272
1 parent 91deea1
commit 34d8272
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diff --git a/include/dlt/dlt_user.h.in b/include/dlt/dlt_user.h.in
@@ -271,6 +271,7 @@ typedef struct
 #ifdef DLT_TRACE_LOAD_CTRL_ENABLE
     pthread_rwlock_t trace_load_limit_lock;
 #endif
+    pid_t local_pid;            /**< Local DltUser process identifier cache */
 } DltUser;
 
 typedef int (*dlt_injection_callback_id)(uint32_t, void *, uint32_t, void *);

diff --git a/src/lib/dlt_user.c b/src/lib/dlt_user.c
@@ -771,6 +771,9 @@ DltReturnValue dlt_init_common(void)
     /* set to unknown state of connected client */
     dlt_user.log_state = -1;
 
+    /* set pid cache to none until we need it */
+    dlt_user.local_pid = -1;
+
     dlt_user.dlt_log_handle = -1;
     dlt_user.dlt_user_handle = DLT_FD_INIT;
 
@@ -4011,7 +4014,10 @@ DltReturnValue dlt_user_log_send_log(DltContextData *log, const int mtype, int *
     /* send session id */
     if (dlt_user.with_session_id) {
         msg.standardheader->htyp |= DLT_HTYP_WSID;
-        msg.headerextra.seid = (uint32_t) getpid();
+        if (__builtin_expect(!!(dlt_user.local_pid == -1), false)) {
+            dlt_user.local_pid = getpid();
+        }
+        msg.headerextra.seid = (uint32_t) dlt_user.local_pid;
     }
 
     if (is_verbose_mode(dlt_user.verbose_mode, log))
@@ -5377,6 +5383,7 @@ static void dlt_fork_child_fork_handler()
     g_dlt_is_child = 1;
     dlt_user_init_state = INIT_UNITIALIZED;
     dlt_user.dlt_log_handle = -1;
+    dlt_user.local_pid = -1;
 #ifdef DLT_TRACE_LOAD_CTRL_ENABLE
     pthread_rwlock_unlock(&trace_load_rw_lock);
 #endif