Messages in this thread |  | | | From | Linus Torvalds <> | | Date | Fri, 2 Mar 2012 16:17:58 -0800 | | Subject | Re: Word-at-a-time dcache name accesses (was Re: .. anybody know of any filesystems that depend on the exact VFS 'namehash' implementation?) |
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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.
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