This is an extremely hot path. Add branch prediction hints to the
error handling and exceptional states to try and squeeze out any
i-cache benefits that GCC can provide.
Tested by recompiling and booting inside QEMU on x86_64.
* kern/ipc_kobject.c (ipc_kobject_server): Use likely and unlikely macros.
---
kern/ipc_kobject.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/kern/ipc_kobject.c b/kern/ipc_kobject.c
index 2e727ae..b0554d6 100644
--- a/kern/ipc_kobject.c
+++ b/kern/ipc_kobject.c
@@ -34,6 +34,7 @@
*/
#include <kern/debug.h>
+#include <kern/macros.h>
#include <kern/printf.h>
#include <mach/port.h>
#include <mach/kern_return.h>
@@ -87,7 +88,7 @@ ipc_kobject_server(ipc_kmsg_t request)
ipc_port_t *destp;
reply = ikm_alloc(reply_size);
- if (reply == IKM_NULL) {
+ if (unlikely(reply == IKM_NULL)) {
printf("ipc_kobject_server: dropping request\n");
ipc_kmsg_destroy(request);
return IKM_NULL;
@@ -179,8 +180,8 @@ ipc_kobject_server(ipc_kmsg_t request)
(*routine)(&request->ikm_header, &reply->ikm_header);
kernel_task->messages_received++;
} else {
- if (!ipc_kobject_notify(&request->ikm_header,
- &reply->ikm_header)) {
+ if (unlikely(!ipc_kobject_notify(&request->ikm_header,
+ &reply->ikm_header))) {
((mig_reply_header_t *) &reply->ikm_header)->RetCode
= MIG_BAD_ID;
#if MACH_IPC_TEST
@@ -226,7 +227,7 @@ ipc_kobject_server(ipc_kmsg_t request)
*destp = IP_NULL;
kr = ((mig_reply_header_t *) &reply->ikm_header)->RetCode;
- if ((kr == KERN_SUCCESS) || (kr == MIG_NO_REPLY)) {
+ if (likely((kr == KERN_SUCCESS) || (kr == MIG_NO_REPLY))) {
/*
* The server function is responsible for the contents
* of the message. The reply port right is moved
@@ -258,7 +259,8 @@ ipc_kobject_server(ipc_kmsg_t request)
ikm_free(reply);
return IKM_NULL;
- } else if (!IP_VALID((ipc_port_t)reply->ikm_header.msgh_remote_port)) {
+ } else if (unlikely(!IP_VALID(
+ (ipc_port_t)reply->ikm_header.msgh_remote_port))) {
/*
* Can't queue the reply message if the destination
* (the reply port) isn't valid.
--
2.53.0
