Messages in this thread | | | Date | Wed, 31 Oct 2012 13:59:16 +0800 | From | Yuanhan Liu <> | Subject | Re: [PATCH 1/2] kfifo: round up the fifo size power of 2 |
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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.liu@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. > > > > ... > > > > --- a/kernel/kfifo.c > > +++ b/kernel/kfifo.c > > @@ -39,11 +39,11 @@ int __kfifo_alloc(struct __kfifo *fifo, unsigned int size, > > size_t esize, gfp_t gfp_mask) > > { > > /* > > - * round down to the next power of 2, since our 'let the indices > > + * round up to the next power of 2, since our 'let the indices > > * wrap' technique works only in this case. > > */ > > if (!is_power_of_2(size)) > > - size = rounddown_pow_of_two(size); > > + size = roundup_pow_of_two(size); > > > > fifo->in = 0; > > fifo->out = 0; > > @@ -84,7 +84,7 @@ int __kfifo_init(struct __kfifo *fifo, void *buffer, > > size /= esize; > > > > 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.
Hi Andrew,
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?
--yliu
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