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Date: Thu, 28 Jun 2007 12:41:15 -0700 (PDT)
From: Jeff Roberson <jroberson@chesapeake.net>
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Subject: Add wakeup_with() before 7.0?
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I propose to add a new api for wakeup before 7.0.  This new api would 
accept a wait channel and a flags argument.  here's the relevant part of 
the diff:

+void   wakeup_with(void *chan, int flags) __nonnull(1);
+#define        WAKEUP_ONE      0x00001         /* Only wakeup on thread. 
*/
+#define        WAKEUP_ALL      0x00002         /* Wake-up all waiters. */
+#define        WAKEUP_LOCAL    0x00004         /* Wake-up on the local 
cpu. */
+#define        WAKEUP_TAIL     0x00008         /* Wake-up the newest 
waiter. */

This allows wakeup callers to hint the scheduler about various 
information.  WAKEUP_LOCAL would allow us to prefer affinity for the 
waking cpu.  I have patches to use this in pipe code and socket buffer 
code that improve performance in some workloads.  WAKEUP_TAIL could be 
used for accept() which I have heard can significantly improve webserver 
performance.

To implement this change sched_wakeup() and setrunnable() need the flags 
plummed all the way through.  I would like feedback on whether people 
think the api breakage should go in now to enable these optimizations for 
7.0, potentially without committing users of these flags right away. 
Alternatively we could break the api later or just skip it until 8.0.

Thanks,
Jeff