On Mon, Feb 17, 2025 at 05:09:34PM +0000, Colin Ian King wrote: > Adding an unlikely() hint on the masked start comparison error > return path improves run-time performance of the mincore system call. > > Benchmarking on an i9-12900 shows an improvement of 7ns on mincore calls > on a 256KB mmap'd region where 50% of the pages we resident. > > Results based on running 20 tests with turbo disabled (to reduce > clock freq turbo changes), with 10 second run per test and comparing > the number of mincores calls per second. The % standard deviation of > the 20 tests was ~0.10%, so results are reliable. I think you've elided _just_ enough information here that nobody can judge whether your stats skills are any good ;-) You've told us 7ns (per call, presumably) and you've told us 0.10% standard deviation, but you haven't told us how long the syscall takes, so nobody can tell whether 7ns is within 0.10% or not ;-) > Signed-off-by: Colin Ian King <colin.i.king@xxxxxxxxx> > --- > mm/mincore.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/mincore.c b/mm/mincore.c > index d6bd19e520fc..832f29f46767 100644 > --- a/mm/mincore.c > +++ b/mm/mincore.c > @@ -239,7 +239,7 @@ SYSCALL_DEFINE3(mincore, unsigned long, start, size_t, len, > start = untagged_addr(start); > > /* Check the start address: needs to be page-aligned.. */ > - if (start & ~PAGE_MASK) > + if (unlikely(start & ~PAGE_MASK)) > return -EINVAL; We might get even more advantage by moving the EINVAL test before untagged_addr() since we know that the tags are all in the high bits and we don't need to have the test be dependent on the previous arithmetic.
