net_generic() function is both a) inline and b) used ~600 times.
It has the following code inside
...
ptr = ng->ptr[id - 1];
...
"id" is never compile time constant so compiler is forced to subtract 1.
And those decrements or LEA [r32 - 1] instructions add up.
We also start id'ing from 1 to catch bugs where pernet sybsystem id
is not initialized and 0. This is quite pointless idea (nothing will
work or immediate interference with first registered subsystem) in
general but it hints what needs to be done for code size reduction.
Namely, overlaying allocation of pointer array and fixed part of
structure in the beginning and using usual base-0 addressing.
Ids are just cookies, their exact values do not matter, so lets start
with 3 on x86_64.
Code size savings (oh boy): -4.2 KB
As usual, ignore the initial compiler stupidity part of the table.
add/remove: 0/0 grow/shrink: 12/670 up/down: 89/-4297 (-4208)
function old new delta
tipc_nametbl_insert_publ 1250 1270 +20
nlmclnt_lookup_host 686 703 +17
nfsd4_encode_fattr 5930 5941 +11
nfs_get_client 1050 1061 +11
register_pernet_operations 333 342 +9
tcf_mirred_init 843 849 +6
tcf_bpf_init 1143 1149 +6
gss_setup_upcall 990 994 +4
idmap_name_to_id 432 434 +2
ops_init 274 275 +1
nfsd_inject_forget_client 259 260 +1
nfs4_alloc_client 612 613 +1
tunnel_key_walker 164 163 -1
...
tipc_bcbase_select_primary 392 360 -32
mac80211_hwsim_new_radio 2808 2767 -41
ipip6_tunnel_ioctl 2228 2186 -42
tipc_bcast_rcv 715 672 -43
tipc_link_build_proto_msg 1140 1089 -51
nfsd4_lock 3851 3796 -55
tipc_mon_rcv 1012 956 -56
Total: Before=156643951, After=156639743, chg -0.00%
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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