From b9420e1c87838bcb354ae3495852430413dd9e4b Mon Sep 17 00:00:00 2001 From: David Laight Date: Fri, 4 Jul 2014 14:35:51 +0000 Subject: [PATCH] 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 Signed-off-by: David S. Miller --- include/net/sctp/command.h | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/include/net/sctp/command.h b/include/net/sctp/command.h index 0e91a42..589a191 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. */ } -- 2.7.4