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It would be nice to know how often we get checksum failures. Even
better, how many of them we can fix with the single bit ecc. So, we add
a statistics structure. The structure can be installed into debugfs
wherever the user wants.
For ocfs2, we'll put it in the superblock-specific debugfs directory and
pass it down from our higher-level functions. The stats are only
registered with debugfs when the filesystem supports metadata ecc.
Signed-off-by: Joel Becker <joel.becker@oracle.com>
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The previous optimization used a fast find-highest-bit-set operation to
give us a good starting point in calc_code_bit(). This version lets the
caller cache the previous code buffer bit offset. Thus, the next call
always starts where the last one left off.
This reduces the calculation another 39%, for a total 80% reduction from
the original, naive implementation. At least, on my machine. This also
brings the parity calculation to within an order of magnitude of the
crc32 calculation.
Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>
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In the calc_code_bit() function, we must find all powers of two beneath
the code bit number, *after* it's shifted by those powers of two. This
requires a loop to see where it ends up.
We can optimize it by starting at its most significant bit. This shaves
32% off the time, for a total of 67.6% shaved off of the original, naive
implementation.
Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>
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When I wrote ocfs2_hamming_encode(), I was following documentation of
the algorithm and didn't have quite the (possibly still imperfect) grasp
of it I do now. As part of this, I literally hand-coded xor. I would
test a bit, and then add that bit via xor to the parity word.
I can, of course, just do a single xor of the parity word and the source
word (the code buffer bit offset). This cuts CPU usage by 53% on a
mostly populated buffer (an inode containing utmp.h inline).
Joel
Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>
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Add block check calls to the read_block validate functions. This is the
almost all of the read-side checking of metaecc. xattr buckets are not checked
yet. Writes are also unchecked, and so a read-write mount will quickly fail.
Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>
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This is the code that computes crc32 and ecc for ocfs2 metadata blocks.
There are high-level functions that check whether the filesystem has the
ecc feature, mid-level functions that work on a single block or array of
buffer_heads, and the low-level ecc hamming code that can handle
multiple buffers like crc32_le().
It's not hooked up to the filesystem yet.
Signed-off-by: Joel Becker <joel.becker@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>
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