Messages in this thread | | | Date | Wed, 16 Mar 2011 10:17:19 -0700 (PDT) | From | Hugh Dickins <> | Subject | Re: [PATCH 1/8] drivers/random: Cache align ip_random better |
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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
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