• Eric Dumazet's avatar
    filter: optimize sk_run_filter · 93aaae2e
    Eric Dumazet authored
    Remove pc variable to avoid arithmetic to compute fentry at each filter
    instruction. Jumps directly manipulate fentry pointer.
    
    As the last instruction of filter[] is guaranteed to be a RETURN, and
    all jumps are before the last instruction, we dont need to check filter
    bounds (number of instructions in filter array) at each iteration, so we
    remove it from sk_run_filter() params.
    
    On x86_32 remove f_k var introduced in commit 57fe93b3
    
    
    (filter: make sure filters dont read uninitialized memory)
    
    Note : We could use a CONFIG_ARCH_HAS_{FEW|MANY}_REGISTERS in order to
    avoid too many ifdefs in this code.
    
    This helps compiler to use cpu registers to hold fentry and A
    accumulator.
    
    On x86_32, this saves 401 bytes, and more important, sk_run_filter()
    runs much faster because less register pressure (One less conditional
    branch per BPF instruction)
    
    # size net/core/filter.o net/core/filter_pre.o
       text    data     bss     dec     hex filename
       2948       0       0    2948     b84 net/core/filter.o
       3349       0       0    3349     d15 net/core/filter_pre.o
    
    on x86_64 :
    # size net/core/filter.o net/core/filter_pre.o
       text    data     bss     dec     hex filename
       5173       0       0    5173    1435 net/core/filter.o
       5224       0       0    5224    1468 net/core/filter_pre.o
    Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
    Acked-by: default avatarChangli Gao <xiaosuo@gmail.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    93aaae2e