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, but to evaluate your suggested change requires a lot more data. Do you plan to do this? Given how _IF_DEQUEUE() is normally used the impact is likely negligible.
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