Em Fri, Dec 13, 2013 at 10:53:35AM +0200, Adrian Hunter escreveu: > My implementation of next_pow2_l() was incorrect. e.g. > perf record -m4296015872 uname > rounding mmap pages size to 17592186044416 bytes (4294967296 pages) > Invalid argument for --mmap_pages/-m > Notice that the next power-of-2 value 4294967296 is less than the > option value 4296015872. > Change to using __builtin_clzl() and prevent the shift being equal to > the width of the operand. Also __builtin_clzl(x) is undefined if x is > 0, so adjust the condition to preclude that possibility. Now:
Can we try to look first if there is an implementation for what we need being used in the kernel sources, in include/ and then try to use, if possible, exactly like done in kernel code? For instance, include/linux/log2.h has roundup_pow_of_two() that seems to be what you need, lemme check... roundup_pow_of_two(4296015872)=8589934592 So, it yields what we need, I'll try to cook up a patch that makes us use it, as I did in my dwarves tools in this changeset: https://git.kernel.org/cgit/devel/pahole/pahole.git/commit/?id=e31fda3063e3c88ca0b93a9fb5e6d6e32478e36b - Arnaldo > perf record -m4296015872 uname > rounding mmap pages size to 35184372088832 bytes (8589934592 pages) > Invalid argument for --mmap_pages/-m > > Signed-off-by: Adrian Hunter <adrian.hun...@intel.com> > --- > tools/perf/util/util.h | 15 ++++++++------- > 1 file changed, 8 insertions(+), 7 deletions(-) > > diff --git a/tools/perf/util/util.h b/tools/perf/util/util.h > index a1eea3e..ae609fe 100644 > --- a/tools/perf/util/util.h > +++ b/tools/perf/util/util.h > @@ -284,13 +284,14 @@ static inline unsigned next_pow2(unsigned x) > > static inline unsigned long next_pow2_l(unsigned long x) > { > -#if BITS_PER_LONG == 64 > - if (x <= (1UL << 31)) > - return next_pow2(x); > - return (unsigned long)next_pow2(x >> 32) << 32; > -#else > - return next_pow2(x); > -#endif > + int leading_zeros; > + > + if (x < 2) > + return 1; > + leading_zeros = __builtin_clzl(x - 1); > + if (!leading_zeros) > + return 0; > + return 1UL << (BITS_PER_LONG - leading_zeros); > } > > size_t hex_width(u64 v); > -- > 1.7.11.7 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
