On Thu, 20 Apr 2017 13:40:57 +0200 Pavel Machek <[email protected]> wrote:
> Hi! > > > > Would it make sense to only do hweight if *bitmap != ~0ULL ? Would it > > > make sense to only check for bitflips > bitflips_threshold each 128 > > > bytes or something like that? > > > > I didn't go as far as you did and simply assumed hweight32/64() were > > already optimized. Feel free to propose extra improvements. > > I'd propose this one (only compile tested, sorry, not sure how to test > this one). If we see ~0UL, there's no need for hweight, and no need to > check number of bitflips. So this should be net win. Looks good to me. Can you send a patch with a real commit message? Thanks, Boris > > Signed-off-by: Pavel Machek <[email protected]> > > diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c > index b0524f8..96c27ec 100644 > --- a/drivers/mtd/nand/nand_base.c > +++ b/drivers/mtd/nand/nand_base.c > @@ -1357,7 +1357,10 @@ static int nand_check_erased_buf(void *buf, int len, > int bitflips_threshold) > > for (; len >= sizeof(long); > len -= sizeof(long), bitmap += sizeof(long)) { > - weight = hweight_long(*((unsigned long *)bitmap)); > + unsigned long d = *((unsigned long *)bitmap); > + if (d == ~0UL) > + continue; > + weight = hweight_long(d); > bitflips += BITS_PER_LONG - weight; > if (unlikely(bitflips > bitflips_threshold)) > return -EBADMSG; >
