CODEWITHSUNDEEP
cgcc
ma08
ma08

Reputation: 3734

Performance under structure packing in C

I am using a 64bit machine

When using the structure

 typedef struct node{
    unsigned int p; //4 bytes
    struct node* next;//8bytes
 }Node;
 //sizeof(Node) is 16 bytes

I know that this is due to structure padding. If I use structure packing using

typedef struct __attribute__((__packed__))
//sizeof(Node) is 12 bytes

Should I expect any performance degradation using packing or is it system dependent?

Compiler is gcc (GCC) 4.4.7

I have tested my code with packed and unpacked structure and there doesn't seem to be any difference in the performance.

Upvotes: 1

Views: 112

Answers (1)

viraptor
viraptor

Reputation: 34145

That's not a lot of information. The answer will also depends on your Node allocation strategy, on whether you embed the node in your data or store it separately, on how big your cache lines are, what kind of work you do, etc.

Measure your runtime with and without packing (in your specific application) - you'll have the answer.

Upvotes: 2

Related Questions