Re: Fw: potential /dev/urandom scalability improvement

[David Mosberger <davidm@napali.hpl.hp.com>]

>>>>> On Thu, 25 Mar 2004 22:19:26 -0600, Matt Mackall <mpm@selenic.com> said:

>  struct entropy_store {
> +	/* mostly-read data: */
> +	struct poolinfo poolinfo;
> +	__u32		*pool;
> +
> +	/* read-write data: */
> +	spinlock_t lock ____cacheline_aligned;
>  	unsigned	add_ptr;
>  	int		entropy_count;
>  	int		input_rotate;
> -	struct poolinfo poolinfo;
> -	__u32		*pool;
> -	spinlock_t lock;
>  };

  Matt> Also, I think in general we'd prefer to stick the aligned bit at the
  Matt> front of the structure rather than at the middle, as we'll avoid extra
  Matt> padding. The size of cachelines is getting rather obscene on some
  Matt> modern processors.

Not sharing the cacheline between the mostly-read data and the
read-write data is the _point_ of this change.  If you reverse the
order, the "poolinfo" and "pool" members will also get invalidated
whenever someone updates the write-intensive data.

	--david