Characterizing Crc Operation on Ceph
summary
Ceph CRC32C work is dominated by many very small operations: for RBD 4K random writes 80% of CRCs are smaller than 292 bytes and for 4K reads 83% are smaller than 254 bytes, with 28 and 41 byte hotspots (preamble_block_t and ceph_msg_header2) making up nearly 40%. BCC Trace on Bluestore-backed RBD (replica 1 and 3) finds small fragmented payload segments, so engineers inline-unfold ceph_crc32c_aarch64 inline assembly and change encoding to reduce tiny segments, yielding about 2% throughput improvement.
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