[PATCH][4/4] poll()/select() timeout behavior

[Bill Rugolsky Jr.]

This patch forces select() to wait *at least* the specified timeout if
no events have occurred, same as poll(). The SUSv3 man page for select(2)
says:

   "If the timeout parameter is not a null pointer, it specifies a maximum
   interval to wait for the selection to complete. If the specified
   time interval expires without any requested operation becoming ready,
   the function shall return."

Additionally:

   "If the requested timeout interval requires a finer granularity than
   the implementation supports, the actual timeout interval shall be
   rounded up to the next supported value."

Unfortunately, fixing the fencepost error places a hard lower limit of
1/HZ on the time slept, and increases the average minimum sleep time
threefold, from 1/(2*HZ) jiffy to 3/(2*HZ).

Please consider applying.

	Bill Rugolsky

--- linux/fs/select.c	2004-02-20 14:29:11.000000000 -0500
+++ linux/fs/select.c	2004-02-20 14:30:18.326814232 -0500
@@ -313,8 +313,8 @@
 		if (sec < 0 || usec < 0 || usec >= 1000000)
 			goto out_nofds;
 
-		if ((unsigned long) sec < (MAX_SCHEDULE_TIMEOUT-1) / HZ - 1) {
-			timeout = ROUND_UP(usec, 1000000/HZ);
+		if ((unsigned long) sec < (MAX_SCHEDULE_TIMEOUT-2) / HZ - 1) {
+			timeout = ROUND_UP(usec, 1000000/HZ) + 1;
 			timeout += sec * (unsigned long) HZ;
 		} else {
 			timeout = MAX_SCHEDULE_TIMEOUT-1;
-
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