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    SubjectRe: Word-at-a-time dcache name accesses (was Re: .. anybody know of any filesystems that depend on the exact VFS 'namehash' implementation?)
    On Fri, Mar 2, 2012 at 4:02 PM, Ted Ts'o <tytso@mit.edu> wrote:
    > Stupid question.  Your patch requires unaligned accesses to not have a
    > heavy penalty, right?  Wasn't it the case that some generations of x86
    > had pretty large penalties for aligned accesses?  Is that something we
    > need to worry about?

    There are basically no x86's with heavy penalties.

    Sure, unaligned accesses are often *slightly* more expensive,
    especially if they cross the cache access boundary (which tends to be
    8 bytes on older 32-bit cpu's, and generally 16 bytes on more modern
    CPUs - so it's not that they are unaligned per se, but that they cross
    the bank size). But even then, it's usually not a huge deal (ie it
    takes up two read slots instead of just one).

    There are x86 chips that are extremely bad at unaligned SSE/MMX
    accesses, but not regular words.

    Linus
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