NACK. I acked it in assumption that Matthew will send v2 that also fixes _find_next_bit_le() the same way. Yury On Thu, Jan 05, 2017 at 05:19:06PM -0800, akpm@xxxxxxxxxxxxxxxxxxxx wrote: > > The patch titled > Subject: lib/find_bit.c: micro-optimise find_next_*_bit > has been added to the -mm tree. Its filename is > find_bit-micro-optimise-find_next__bit.patch > > This patch should soon appear at > http://ozlabs.org/~akpm/mmots/broken-out/find_bit-micro-optimise-find_next__bit.patch > and later at > http://ozlabs.org/~akpm/mmotm/broken-out/find_bit-micro-optimise-find_next__bit.patch > > Before you just go and hit "reply", please: > a) Consider who else should be cc'ed > b) Prefer to cc a suitable mailing list as well > c) Ideally: find the original patch on the mailing list and do a > reply-to-all to that, adding suitable additional cc's > > *** Remember to use Documentation/SubmitChecklist when testing your code *** > > The -mm tree is included into linux-next and is updated > there every 3-4 working days > > ------------------------------------------------------ > From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx> > Subject: lib/find_bit.c: micro-optimise find_next_*_bit > > This saves 20 bytes on my x86-64 build, mostly due to alignment > considerations ... I think it actually saves about five bytes of > instructions. There's really two parts to this commit. First, the first > half of the test: (!nbits || start >= nbits) is trivially a subset of the > second half, since nbits and start are both unsigned. Second, while > looking at the disassembly, I noticed that GCC was predicting the branch > taken. Since this is a failure case, it's clearly the less likely of the > two branches, so add an unlikely() to override GCC's heuristics. > > Link: http://lkml.kernel.org/r/1482513603-9630-1-git-send-email-mawilcox@xxxxxxxxxxxxxxxxx > Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx> > Acked-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx> > Acked-by: Yury Norov <ynorov@xxxxxxxxxxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > --- > > lib/find_bit.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff -puN lib/find_bit.c~find_bit-micro-optimise-find_next__bit lib/find_bit.c > --- a/lib/find_bit.c~find_bit-micro-optimise-find_next__bit > +++ a/lib/find_bit.c > @@ -33,7 +33,7 @@ static unsigned long _find_next_bit(cons > { > unsigned long tmp; > > - if (!nbits || start >= nbits) > + if (unlikely(start >= nbits)) > return nbits; > > tmp = addr[start / BITS_PER_LONG] ^ invert; > _ > > Patches currently in -mm which might be from mawilcox@xxxxxxxxxxxxx are > > find_bit-micro-optimise-find_next__bit.patch > reimplement-idr-and-ida-using-the-radix-tree-support-storing-null-in-the-idr.patch -- 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
