Servus, while working on an improved TLB flush logic for s390 I noticed that for s390 cpumask_equal() alias bitmap_equal() can be improved for the special case "(nbits % BITS_PER_LONG) == 0". The memcmp function can be used in this case and we have an instruction for that .. Trouble is that the default memcmp implementation uses a byte loop while the __bitmap_equal function uses a loop over unsigned long. For x86 the __bitmap_equal function is faster than memcmp, using memcmp for the special case for all architectures is not correct. Right now the patches uses a '#ifdef CONFIG_S390' to guard the memcmp special case. I hesitate to put another CONFIG_S390 into common code, alternatively __HAVE_ARCH_MEMCMP could be used. There are 7 architectures with the define: arc, arm64, blackfin, frv, powerpc, s390 and sparc. Of those I guess only powerpc, s390 and sparc will have configs with (NR_CPUS > BITS_PER_LONG). For (NR_CPUS <= BITS_PER_LONG) the xor optimization is used. powerpc, s390 and sparc do have optimized memcmp code, the question is if it is faster then __bitmap_equal. Now, CONFIG_S390 or __HAVE_ARCH_MEMCMP ? blue skies, Martin -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
