Add wakeup_with() before 7.0?

[John Baldwin]

On Thursday 28 June 2007 03:41:15 pm Jeff Roberson wrote:
> 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.

We have something like WAKEUP_TAIL (but different, it also prefers non-swapped 
out processes in addition to taking the most recently suspended thread) at 
work for accept() and it just modifies the sleepq code's choice in 
sleepq_signal() of which thread to pick, it doesn't touch any of the 
scheduler stuff at all.  OTOH, I think the scheduler ABIs are ok to change 
during 7.x as they aren't exposed to any KLD's (no well-behaving ones anyway) 
as drivers, etc. should all be using higher-level APIs like cv_*() or 
*sleep().

-- 
John Baldwin