• Ondrej Mosnacek's avatar
    crypto: xts - Drop use of auxiliary buffer · 78105c7e
    Ondrej Mosnacek authored
    Since commit acb9b159 ("crypto: gf128mul - define gf128mul_x_* in
    gf128mul.h"), the gf128mul_x_*() functions are very fast and therefore
    caching the computed XTS tweaks has only negligible advantage over
    computing them twice.
    
    In fact, since the current caching implementation limits the size of
    the calls to the child ecb(...) algorithm to PAGE_SIZE (usually 4096 B),
    it is often actually slower than the simple recomputing implementation.
    
    This patch simplifies the XTS template to recompute the XTS tweaks from
    scratch in the second pass and thus also removes the need to allocate a
    dynamic buffer using kmalloc().
    
    As discussed at [1], the use of kmalloc causes deadlocks with dm-crypt.
    
    PERFORMANCE RESULTS
    I measured time to encrypt/decrypt a memory buffer of varying sizes with
    xts(ecb-aes-aesni) using a tool I wrote ([2]) and the results suggest
    that after this patch the performance is either better or comparable for
    both small and large buffers. Note that there is a lot of noise in the
    measurements, but the overall difference is easy to see.
    
    Old code:
           ALGORITHM KEY (b)        DATA (B)   TIME ENC (ns)   TIME DEC (ns)
            xts(aes)     256              64             331             328
            xts(aes)     384              64             332             333
            xts(aes)     512              64             338             348
            xts(aes)     256             512             889             920
            xts(aes)     384             512            1019             993
            xts(aes)     512             512            1032             990
            xts(aes)     256            4096            2152            2292
            xts(aes)     384            4096            2453            2597
            xts(aes)     512            4096            3041            2641
            xts(aes)     256           16384            9443            8027
            xts(aes)     384           16384            8536            8925
            xts(aes)     512           16384            9232            9417
            xts(aes)     256           32768           16383           14897
            xts(aes)     384           32768           17527           16102
            xts(aes)     512           32768           18483           17322
    
    New code:
           ALGORITHM KEY (b)        DATA (B)   TIME ENC (ns)   TIME DEC (ns)
            xts(aes)     256              64             328             324
            xts(aes)     384              64             324             319
            xts(aes)     512              64             320             322
            xts(aes)     256             512             476             473
            xts(aes)     384             512             509             492
            xts(aes)     512             512             531             514
            xts(aes)     256            4096            2132            1829
            xts(aes)     384            4096            2357            2055
            xts(aes)     512            4096            2178            2027
            xts(aes)     256           16384            6920            6983
            xts(aes)     384           16384            8597            7505
            xts(aes)     512           16384            7841            8164
            xts(aes)     256           32768           13468           12307
            xts(aes)     384           32768           14808           13402
            xts(aes)     512           32768           15753           14636
    
    [1] https://lkml.org/lkml/2018/8/23/1315
    [2] https://gitlab.com/omos/linux-crypto-benchSigned-off-by: 's avatarOndrej Mosnacek <omosnace@redhat.com>
    Signed-off-by: 's avatarHerbert Xu <herbert@gondor.apana.org.au>
    78105c7e
xts.c 9.02 KB