| Message ID | 20141202084313.18411.qmail@ns.horizon.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Herbert Xu |
| Headers | show |
On Tue, Dec 02, 2014 at 03:43:13AM -0500, George Spelvin wrote: > rand_read_pos is never more than 16, while there's only 1 flag > bit allocated, so we can shrink the context a little. > > Signed-off-by: George Spelvin <linux@horizon.com> > --- > crypto/ansi_cprng.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > They're also reordered to avoid alignment holes. > > diff --git a/crypto/ansi_cprng.c b/crypto/ansi_cprng.c > index 93ed00f6..f40f54cd 100644 > --- a/crypto/ansi_cprng.c > +++ b/crypto/ansi_cprng.c > @@ -51,9 +51,9 @@ struct prng_context { > unsigned char rand_data[DEFAULT_BLK_SZ]; > unsigned char DT[DEFAULT_BLK_SZ]; > unsigned char V[DEFAULT_BLK_SZ]; > - u32 rand_read_pos; /* Offset into rand_data[] */ > + unsigned char rand_read_pos; /* Offset into rand_data[] */ u8 please. Also, not sure if this helps much, as I think the padding will just get you back to word alignment on each of these. > + unsigned char flags; > struct crypto_cipher *tfm; > - u32 flags; > }; > > static int dbg; > -- > 2.1.3 > > -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
>> --- a/crypto/ansi_cprng.c >> +++ b/crypto/ansi_cprng.c >> @@ -51,9 +51,9 @@ struct prng_context { >> unsigned char rand_data[DEFAULT_BLK_SZ]; >> unsigned char DT[DEFAULT_BLK_SZ]; >> unsigned char V[DEFAULT_BLK_SZ]; >> - u32 rand_read_pos; /* Offset into rand_data[] */ >> + unsigned char rand_read_pos; /* Offset into rand_data[] */ > u8 please. Also, not sure if this helps much, as I think the padding > will just get you back to word alignment on each of these. I noticed the "unsigned char" vs "u8" issue, but didn't make the change as I didn't think the readailility improvement was worth the code churn. But I'd be happy to clean that up, too! Should I convert all the buffers and function prototypes, or is there some criterion for distinguishing which gets which? (E.g. buffers are "unsigned char" but control variables are "u8".) And actually, you do win. spinlock_t is 16 bits on x86, and the buffers are all 16 bytes. (80 bytes before my earlier patches, 48 bytes after.) So the the structure goes from: 32-bit 64-bit Variable Offset Size Offset Size 0 2 0 2 spinlock_t prng_lock 2 16 2 16 unsigned char rand_data[16] 18 16 18 16 unsigned char DT[16] 34 16 34 16 unsigned char V[16] 50 2 50 2 (alignemnt) 52 4 52 4 u32 rand_read_pos 56 4 56 8 struct crypto_cipher *tfm 60 4 64 4 u32 flags 68 4 (alignment) 64 72 (structure size) to 32-bit 64-bit Variable Offset Size Offset Size 34 16 34 16 unsigned char V[16] 50 1 50 1 u8 rand_read_pos 51 1 51 1 u8 flags 52 4 (alignment) 52 4 56 8 struct crypto_cipher *tfm 56 64 (structure size) You still get 4 bytes of alignment padding on x86-64, but given that the structure has 60 bytes of payload, that's the minimum possible. You save 6 bytes of variables and 2 bytes of padding on both 32- and 64-bit systems, for a total of 8 bytes, and that's enough to knock you into a smaller slab object bin on 64-bit. I forget where I read the terminology, but the most efficient wat to pack a structure is in an "organ pipe" configuraiton where the biggest (in terms of *alignment*) members are on the outside and the structre and the smaller elements are on the inside. Putting a 32-bit "flags" after a 64-bit pointer violates that. -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, Dec 02, 2014 at 03:28:17PM -0500, George Spelvin wrote: > >> --- a/crypto/ansi_cprng.c > >> +++ b/crypto/ansi_cprng.c > >> @@ -51,9 +51,9 @@ struct prng_context { > >> unsigned char rand_data[DEFAULT_BLK_SZ]; > >> unsigned char DT[DEFAULT_BLK_SZ]; > >> unsigned char V[DEFAULT_BLK_SZ]; > >> - u32 rand_read_pos; /* Offset into rand_data[] */ > >> + unsigned char rand_read_pos; /* Offset into rand_data[] */ > > > u8 please. Also, not sure if this helps much, as I think the padding > > will just get you back to word alignment on each of these. > > I noticed the "unsigned char" vs "u8" issue, but didn't make the change > as I didn't think the readailility improvement was worth the code churn. > You just sent a 17 patch series of clean up and were worried about code churn converting an unsigned char to a u8? > But I'd be happy to clean that up, too! > > Should I convert all the buffers and function prototypes, or is there > some criterion for distinguishing which gets which? (E.g. buffers are > "unsigned char" but control variables are "u8".) > If you want to sure. u8 probably makes more sense for the buffers here as our intent is to treat them as an array of byte values. > And actually, you do win. spinlock_t is 16 bits on x86, > and the buffers are all 16 bytes. (80 bytes before my earlier > patches, 48 bytes after.) > > So the the structure goes from: > > 32-bit 64-bit Variable > Offset Size Offset Size > 0 2 0 2 spinlock_t prng_lock > 2 16 2 16 unsigned char rand_data[16] > 18 16 18 16 unsigned char DT[16] > 34 16 34 16 unsigned char V[16] > 50 2 50 2 (alignemnt) > 52 4 52 4 u32 rand_read_pos > 56 4 56 8 struct crypto_cipher *tfm > 60 4 64 4 u32 flags > 68 4 (alignment) > 64 72 (structure size) > > to > > 32-bit 64-bit Variable > Offset Size Offset Size > 34 16 34 16 unsigned char V[16] > 50 1 50 1 u8 rand_read_pos > 51 1 51 1 u8 flags > 52 4 (alignment) > 52 4 56 8 struct crypto_cipher *tfm > 56 64 (structure size) > > You still get 4 bytes of alignment padding on x86-64, but given that > the structure has 60 bytes of payload, that's the minimum possible. > > You save 6 bytes of variables and 2 bytes of padding on both > 32- and 64-bit systems, for a total of 8 bytes, and that's enough > to knock you into a smaller slab object bin on 64-bit. > > > I forget where I read the terminology, but the most efficient > wat to pack a structure is in an "organ pipe" configuraiton where > the biggest (in terms of *alignment*) members are on the outside > and the structre and the smaller elements are on the inside. > Putting a 32-bit "flags" after a 64-bit pointer violates that. > -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/crypto/ansi_cprng.c b/crypto/ansi_cprng.c index 93ed00f6..f40f54cd 100644 --- a/crypto/ansi_cprng.c +++ b/crypto/ansi_cprng.c @@ -51,9 +51,9 @@ struct prng_context { unsigned char rand_data[DEFAULT_BLK_SZ]; unsigned char DT[DEFAULT_BLK_SZ]; unsigned char V[DEFAULT_BLK_SZ]; - u32 rand_read_pos; /* Offset into rand_data[] */ + unsigned char rand_read_pos; /* Offset into rand_data[] */ + unsigned char flags; struct crypto_cipher *tfm; - u32 flags; }; static int dbg;
rand_read_pos is never more than 16, while there's only 1 flag bit allocated, so we can shrink the context a little. Signed-off-by: George Spelvin <linux@horizon.com> --- crypto/ansi_cprng.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) They're also reordered to avoid alignment holes.