Messages in this thread | | | Subject | Re: [PATCH v1 00/16] ext4: Add metadata checksumming | From | "Martin K. Petersen" <> | Date | Sun, 04 Sep 2011 18:19:16 -0400 |
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>>>>> "Andi" == Andi Kleen <andi@firstfloor.org> writes:
Andi> Doesn't have any performance numbers.
It's been a while since I read them. I thought they had some compelling numbers. Anyway, made a big difference in real life testing here. For sustained I/O we're talking an order of magnitude.
Andi> You need to keep in mind that PCLMULQDQ uses FPU state, so any Andi> speedup for the kernel must be large enough to amortize the cost Andi> of saving the FPU state.
Yeah, my test cases were for bulk database I/O, not for writing a handful of fs metadata blocks. Plus for the DB tests the CRC was generated in userland.
I seem to recall Joel picking something other than the hw-accelerated CRC32C for ocfs2 metadata and that didn't cause any problems.
That said, I do see a difference between IP checksum and CRC on normal FS workloads with DIX enabled here.
Andi> Typically that only works out for quite large buffers, but kernel Andi> buffers are relatively small.
*nod*
-- Martin K. Petersen Oracle Linux Engineering
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