Jan Engelhardt wrote:
On Tuesday 2008-04-01 14:49, Patrick McHardy wrote:
Jan Engelhardt wrote:
[NETFILTER]: xt_hashlimit: add workaround for >>32 case
Hardware surprisingly does nothing when a 32-bit right-shift is
to be done. Worse yet, compilers do not even work around it.
Thats because the C standard states that the result is undefined.
Anyways, I think this patch is slightly nicer because it
gets rid of the double negation and the %32 == 0 special-casing
for IPv6.
Do you want to add an ACKed-by?
The special casing for %32==0 in the IPv6 block was not a workaround for
'>>32', but speed.
I'm aware of that.
Assuming the C code is already perfect and gets
transformed 1:1 into assembly without any further optimization, the cost
of the operation is 4 simple 'mov' instructions for %32==0, whereas
calling maskl() will involve a fair number of operations (at least 27 by
the count). [With your patch, maskl() is now 28 + a branch.]
The "optimization" results in bigger code and more branches itself.
Just removing it without fixing maskl reduces code size by over 35%:
net/netfilter/xt_hashlimit.c:
hashlimit_ipv6_mask | -103 # 274 -> 171
1 function changed, 103 bytes removed
Fixing maskl bloats it up again, but still a net win:
hashlimit_ipv6_mask | -9 # 274 -> 265, size inlines: 71 -> 148
hashlimit_init_dst | +6 # 589 -> 595, size inlines: 86 -> 106
2 functions changed, 6 bytes added, 9 bytes removed, diff: -3
Just the maskl fix results in:
net/netfilter/xt_hashlimit.c:
hashlimit_ipv6_mask | +95 # 274 -> 369, size inlines: 71 -> 143
hashlimit_init_dst | +6 # 589 -> 595, size inlines: 86 -> 106
2 functions changed, 101 bytes added
--
To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
