From: Jesse Barnes <jbarnes@engr.sgi.com>
To: Guillaume Thouvenin <guillaume.thouvenin@bull.net>
Subject: Re: [patch 1/2] fork_connector: add a fork connector
Date: Thu, 17 Mar 2005 08:56:57 -0800
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On Thursday, March 17, 2005 1:04 am, Guillaume Thouvenin wrote:
> +static inline void fork_connector(pid_t parent, pid_t child)
> +{
> + static DEFINE_SPINLOCK(cn_fork_lock);
> + static __u32 seq;   /* used to test if message is lost */
> +
> + if (cn_fork_enable) {
> +  struct cn_msg *msg;
> +
> +  __u8 buffer[CN_FORK_MSG_SIZE];
> +
> +  msg = (struct cn_msg *)buffer;
> +
> +  memcpy(&msg->id, &cb_fork_id, sizeof(msg->id));
> +  spin_lock(&cn_fork_lock);
> +  msg->seq = seq++;
> +  spin_unlock(&cn_fork_lock);

As I mentioned before, this won't work very well on a large CPU count system.  
cn_fork_lock will be taken by each CPU everytime it does a fork, meaning that 
forks will be very slow if lots of CPUs are doing them at the same time.  Is 
there a more scalable way to ensure message delivery?

Jesse
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