Re: [PATCH 1/8] drivers/random: Cache align ip_random better
From: Hugh Dickins <hughd@google.com>
Date: 2011-03-16 17:17:42
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On Sun, 13 Mar 2011, George Spelvin wrote:
quoted hunk ↗ jump to hunk
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@kvack.org. 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@kvack.org"> email@kvack.org </a>