[lkml]   [2007]   [Mar]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: [patch v2] epoll use a single inode ...

    On Tue, 6 Mar 2007, H. Peter Anvin wrote:
    > That's true for *any* sprintf(), though. sprintf() converts all its arguments
    > to 64 bits.

    Well, it very much uses "do_div()", so that it can do a

    64 / 32 -> (div64,mod32)

    divide, which is often faster than a full 64:64 divide.

    > However, this could be optimized. I think right now sprintf() uses a generic
    > divide-by-base, but a divide by 8 and 16 can of course be handled with a
    > shift, and divide by 10 can be replaced with a multiplication by
    > 0x1999999999999999ULL on most architectures.

    Nope. You need both the result of the division *and* the remainder, and
    you can't do that with a single multiply.

    Also, with modern hardware, divides are usually fairly cheap, with early
    exit logic, so that the common case of small integers is fairly cheap.
    Yeah, generating a full 64-bit number printout is still expensive, of
    course (both because you need to do many divides *and* because only the
    last few divides will be able to do any appreciable early exit logic.

    Anyway, I think a full integer divide on Core 2 is something like 22
    cycles. Yes, the multiply is much fasster (at 4 cycles), but I think that
    22 cycles is actually worst-case.

    Somebody who has a benchmark could try.

    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to
    More majordomo info at
    Please read the FAQ at

     \ /
      Last update: 2007-03-06 18:13    [W:0.022 / U:37.448 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site