Am Mittwoch, den 31.10.2012, 13:59 +0800 schrieb Yuanhan Liu: > On Mon, Oct 29, 2012 at 01:59:35PM -0700, Andrew Morton wrote: > > On Fri, 26 Oct 2012 15:56:57 +0800 > > Yuanhan Liu <yuanhan....@linux.intel.com> wrote: > > > > > Say, if we want to allocate a filo with size of 6 bytes, it would be safer > > > to allocate 8 bytes instead of 4 bytes. > > > > > > ... > > > if (!is_power_of_2(size)) > > > - size = rounddown_pow_of_two(size); > > > + size = roundup_pow_of_two(size); > > > > > > fifo->in = 0; > > > fifo->out = 0; > > > > hm, well, if the user asked for a 100-element fifo then it is a bit > > strange and unexpected to give them a 128-element one. > > > Yes, and I guess the same to give them a 64-element one. > > > > > If there's absolutely no prospect that the kfifo code will ever support > > 100-byte fifos then I guess we should rework the API so that the caller > > has to pass in log2 of the size, not the size itself. That way there > > will be no surprises and no mistakes. > > > > That being said, the power-of-2 limitation isn't at all intrinsic to a > > fifo, so we shouldn't do this. Ideally, we'd change the kfifo > > implementation so it does what the caller asked it to do! > > I'm fine with removing the power-of-2 limitation. Stefani, what's your > comment on that? >
You can't remove the power-of-2-limitation, since this would result in a performance decrease (bit wise and vs. modulo operation). Andrew is right, this is an API miss design. So it would be good to rework the kfifo_init () and kfifo_alloc() to pass in log2 of the size, not the size itself. Stefani -- 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/
