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Differential D4055 Diff 9898 sys/dev/cxgb/ulp/tom/cxgb_listen.c

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sys/dev/cxgb/ulp/tom/cxgb_listen.c

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INP_WLOCK_ASSERT(new_inp); INP_WLOCK_ASSERT(new_inp);
if (__predict_false(!(synqe->flags & TP_SYNQE_EXPANDED))) { if (__predict_false(!(synqe->flags & TP_SYNQE_EXPANDED))) {
tcp_timer_activate(intotcpcb(new_inp), TT_KEEP, 0); struct tcpcb *tp;
tp = intotcpcb(new_inp);
tcp_timer_activate(tp, TT_KEEP, 0);
jtlUnsubmitted
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Why store tp locally? There is a cost to adding it to the stack.

jtl: Why store tp locally? There is a cost to adding it to the stack.
rrsAuthorUnsubmitted
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Ok I have changed this, but do you really think that the compiler with
-O2 would not optimize it.. I do things to *make it clear* whats going on
in code. No matter if you do

{

tp = foomacro()
 do_someting(tp)

}

or

{

do_something(foomacro())

}

The compiler underneath will optimize out such behavior.. and I do
think the old way illustrates clarity in what is going on with the code but
I am ambivalent about it in general so I changed it :-)

rrs: Ok I have changed this, but do you really think that the compiler with -O2 would not optimize…
jtlUnsubmitted
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Ok I have changed this, but do you really think that the compiler with

-O2 would not optimize it..

I would hope so, but I've seen compilers fail to optimize out assignments like this. In one case, we picked up a several percent performance gain by removing a variable assignment like this from a function in a critical path in one of our internal kernel modules.

So, while it is nice to trust the compiler to optimize, I prefer to help the compiler along when we can do so without sacrificing clarity. I think this is one of those cases.

jtl: > Ok I have changed this, but do you really think that the compiler with -O2 would not optimize…
t3_offload_socket(tod, synqe, so); t3_offload_socket(tod, synqe, so);
} }
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