Messages in this thread | | | Subject | Re: [PATCH 1/8] drivers/random: Cache align ip_random better | From | Matt Mackall <> | Date | Wed, 16 Mar 2011 13:23:07 -0500 |
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On Wed, 2011-03-16 at 10:17 -0700, Hugh Dickins wrote: > 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?
I think this alignment exists to minimize the number of cacheline bounces on SMP as this can be a pretty hot structure in the network stack. It could probably benefit from a per-cpu treatment.
-- Mathematics is the supreme nostalgia of our time.
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