Bruce M. Simpson wrote:
rihad wrote:
Not sure if this is a worthwhile optimization? FreeBSD 7.0
--- /usr/src/sys/net/if_var.h 2007-12-07 09:46:08.000000000 +0400
+++ if_var.h 2008-05-30 18:10:25.000000000 +0500
@@ -282,7 +282,8 @@
if (m) { \
if (((ifq)->ifq_head = (m)->m_nextpkt) == NULL) \
(ifq)->ifq_tail = NULL; \
- (m)->m_nextpkt = NULL; \
+ else \
+ (m)->m_nextpkt = NULL; \
(ifq)->ifq_len--; \
} \
} while (0)
It could save dirtying an L2 data cache line at the expense of taking a
conditional branch,
Whoa, why don't you take it easy on me :) I'm not that much into kernel
(or hardware) programming. It's just that reading Ch. 3 of TCP/IP
Illustrated Vol.2 by Rich Stevens got me digging around FreeBSD source
code dealing with struct ifnet, where this piece of code caught my
attention.
but to evaluate your suggested change requires a lot
more data. Do you plan to do this?
Perhaps there is already a framework for trying out changes in -CURRENT
and seeing their relative impact, so perhaps someone more experienced
than I am can see to this?
Given how _IF_DEQUEUE() is normally
used the impact is likely negligible.
Oh, I see. A nice first attempt of mine anyway ;) Thanks.
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