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| author | David Laight <David.Laight@ACULAB.COM> | 2014-07-04 18:35:51 +0400 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2014-07-09 01:39:00 +0400 |
| commit | b9420e1c87838bcb354ae3495852430413dd9e4b (patch) | |
| tree | b0dd1a9022cf37626cd70cdc5f15f7c8507b7647 /include/net/sctp/command.h | |
| parent | be1f4f48cef17c6ea9350db04c774dc8eb252158 (diff) | |
| download | linux-b9420e1c87838bcb354ae3495852430413dd9e4b.tar.xz | |
net: sctp: Optimise the way 'sctp_arg_t' values are initialised.
Even if memset() is inlined (as on x86) using it to zero the union
generates a memory word write of zero, followed by a write of the
smaller field, and then a read of the word.
As well as being a lot of instructions the sequence is unlikely to
be optimised by the store-load forward hardware so will be slow.
Instead allocate a field of the union that is the same size as the
entire union and write a zero value to it. The compiler will then
generate the required value in a register.
Zeroing the union shouldn't be necessary, but this patch series isn't
intended to have a behavioural change.
Signed-off-by: David Laight <david.laight@aculab.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/net/sctp/command.h')
| -rw-r--r-- | include/net/sctp/command.h | 8 |
1 files changed, 5 insertions, 3 deletions
diff --git a/include/net/sctp/command.h b/include/net/sctp/command.h index 0e91a42065db..589a1918ad55 100644 --- a/include/net/sctp/command.h +++ b/include/net/sctp/command.h @@ -118,6 +118,7 @@ typedef enum { #define SCTP_MAX_NUM_COMMANDS 14 typedef union { + void *zero_all; /* Set to NULL to clear the entire union */ __s32 i32; __u32 u32; __be32 be32; @@ -154,7 +155,7 @@ typedef union { static inline sctp_arg_t \ SCTP_## name (type arg) \ { sctp_arg_t retval;\ - memset(&retval, 0, sizeof(sctp_arg_t));\ + retval.zero_all = NULL;\ retval.elt = arg;\ return retval;\ } @@ -191,7 +192,7 @@ static inline sctp_arg_t SCTP_NOFORCE(void) static inline sctp_arg_t SCTP_NULL(void) { sctp_arg_t retval; - memset(&retval, 0, sizeof(sctp_arg_t)); + retval.zero_all = NULL; return retval; } @@ -212,7 +213,8 @@ typedef struct { */ static inline int sctp_init_cmd_seq(sctp_cmd_seq_t *seq) { - memset(seq, 0, sizeof(sctp_cmd_seq_t)); + seq->next_free_slot = 0; + seq->next_cmd = 0; return 1; /* We always succeed. */ } |