Eric W. Biederman a écrit :
Eric Dumazet <[EMAIL PROTECTED]> writes:
Definitly wanted here. Thank you.
One more refcounting on each socket creation/deletion was expensive.
Really? Have you actually measured that? If the overhead is
measurable and expensive we may want to look at per cpu counters or
something like that. So far I don't have any numbers that say any
of the network namespace work inherently has any overhead.
It seems that on some old opterons (two 246 for example),
"if (atomic_dec_and_test(&net->count))" is rather expensive yes :(
I am not sure per cpu counters help : I tried this and got no speedup. (This
was on net_device refcnt at that time)
(on this machines, the access through fs/gs selector seems expensive too)
Maybe a lazy mode could be done, ie only do a atomic_dec(), as done in
dev_put() ?
Also, "count" sits in a cache line that contains mostly read and shared
fields, you might want to put it in a separate cache line in SMP, to avoid
cache line ping-pongs.
Maybe we can add a macro to get nd_net from a "struct net_device"
so that every instance of
if (dev->nd_net != &init_net)
goto drop;
can also be optimized away if !CONFIG_NET_NS
Well that extra check should be removed once we finish converting
those code paths. So I'm not too worried.
OK. Since the conditional test can be predicted by cpu, it certainly doesnt
matter.
If this becomes a big issue I can dig up my old code that
replaced struct net * with a net_t typedef and used functions
for all of the comparisons and allowed everything to be compiled
away.
Trouble was it was sufficiently different that it was just enough
different that people could not immediately understand the code.
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