On Sun, 13 Mar 2011, George Spelvin wrote:
> Cache aligning the secret[] buffer makes copying from it infinitesimally
> more efficient.
> ---
> drivers/char/random.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 72a4fcb..4bcc4f2 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -1417,8 +1417,8 @@ static __u32 twothirdsMD4Transform(__u32 const buf[4], __u32 const in[12])
> #define HASH_MASK ((1 << HASH_BITS) - 1)
>
> static struct keydata {
> - __u32 count; /* already shifted to the final position */
> __u32 secret[12];
> + __u32 count; /* already shifted to the final position */
> } ____cacheline_aligned ip_keydata[2];
>
> static unsigned int ip_cnt;
I'm intrigued: please educate me. On what architectures does cache-
aligning a 48-byte buffer (previously offset by 4 bytes) speed up
copying from it, and why? Does the copying involve 8-byte or 16-byte
instructions that benefit from that alignment, rather than cacheline
alignment?
Thanks,
Hugh
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxxx For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>