On 04/17/2013 05:26 AM, Daniel Borkmann wrote:
On 04/17/2013 10:43 AM, David Laight wrote:
__u32 outstanding_bytes;
- /* Are we doing fast-rtx on this queue */
- char fast_rtx;
-
- /* Corked? */
- char cork;
-
- /* Is this structure empty? */
- char empty;
+ __u8 fast_rtx:1, /* Are we doing fast-rtx on this queue */
+ cork:1, /* Corked? */
+ empty:1; /* Is this structure empty? */
};
Use of bitfields just makes the code slower.
The only real excuse for using them is to reduce the size
of a structure that is allocated a lot.
sctp_outq is _embedded_ into an sctp_association structure, which
has [size: 2280, cachelines: 36, members: 76]! A next step would be
to try to reorder its elements carefully and see if we can reduce
the size by filling some holes.
I remember attempting this undertaking that led me down the rabbit hole
so fast that my head started to spin. It is a badly needed project, but
be prepared to spend a lot of time on it.
Not sure if the space saving is worth the bad code generated for
bit-fields, especially considering that empty and cork are used on
almost every packet.
-vlad
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