Messages in this thread | | | Date | Thu, 8 Apr 2010 20:26:54 +0200 | From | Ingo Molnar <> | Subject | Re: [GIT PULL] scheduler fix |
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* Andreas Schwab <schwab@redhat.com> wrote:
> Linus Torvalds <torvalds@linux-foundation.org> writes: > > > On Thu, 8 Apr 2010, Ingo Molnar wrote: > >> > >> - if (len < nr_cpu_ids) > >> + if ((len * BITS_PER_BYTE) < nr_cpu_ids) > >> return -EINVAL; > > > > Not that it really matters, but this will now fail for no good reason if > > you pass it a half-gigabyte area due to overflow. > > Which can easily be avoided. > > if (len < DIV_ROUND_UP(nr_cpu_ids, BITS_PER_BYTE))
nr_cpu_ids is a signed integer which turns the DIV_ROUND_UP into a somewhat suboptimal instruction sequence. (havent checked it though)
So i'd suggest changing nr_cpu_ids to unsigned int [unless there's some strong reason to have it signed] plus doing something like:
if (len < (nr_cpu_ids >> BITS_PER_BYTE_BITS))
ought to both result in better code and should be more readable. We'd have to add:
#define BITS_PER_BYTE_BITS 3
to linux/bitops.h.
Ingo
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