Re: [PATCH] Microoptimization of lib/poll.c

[Bruno Haible]

Paolo Bonzini wrote:
> I actually noticed these in a profile!

What tool do you use for doing profiling on a per-line or per-instruction
basis? The Google profiler?

> 3) access to thread-local errno is slow, it's also better to cache it.

Pheww! That is micro-optimization indeed.

Do you have an objection against this further patch? Should save 2 instructions
in the case that you were not profiling.

--- lib/poll.c.orig     2008-08-06 15:11:42.000000000 +0200
+++ lib/poll.c  2008-08-06 15:07:43.000000000 +0200
@@ -55,7 +55,7 @@
      int timeout;
 {
   fd_set rfds, wfds, efds;
-  struct timeval tv = { 0, 0 };
+  struct timeval tv;
   struct timeval *ptv;
   int maxfd, rc;
   nfds_t i;
@@ -91,7 +91,11 @@
 
   /* convert timeout number into a timeval structure */
   if (timeout == 0)
-    ptv = &tv;
+    {
+      ptv = &tv;
+      ptv->tv_sec = 0;
+      ptv->tv_usec = 0;
+    }
   else if (timeout > 0)
     {
       ptv = &tv;