On 03/31/2012 04:38 AM, John Robinson wrote: > On 29/03/2012 22:44, Jim Kukunas wrote: >> Based on xor_speed, the AVX implementation appears to be ~32% faster >> than the >> SSE implementation on my i7 2600: >> >> generic_sse: 15088.000 MB/sec >> avx: 19936.000 MB/sec > > I just noticed in my logs the other day (recent el5 kernel on a Core 2): > > raid5: automatically using best checksumming function: generic_sse > generic_sse: 7805.000 MB/sec > raid5: using function: generic_sse (7805.000 MB/sec) > raid6: int64x1 2635 MB/s > raid6: int64x2 3208 MB/s > raid6: int64x4 3020 MB/s > raid6: int64x8 2519 MB/s > raid6: sse2x1 5099 MB/s > raid6: sse2x2 5742 MB/s > raid6: sse2x4 8237 MB/s > raid6: using algorithm sse2x4 (8237 MB/s) > > I was just wondering how it's possible to do the RAID6 Q calculation > faster than the RAID5 XOR calculation - or am I reading this log excerpt > wrongly? > > It's probably academic, since the machine this is running on only has a > maximum of about 4500 MB/s of memory throughput, and a lot of that would > be consumed sending data to disc in amongst the calculations being done. > It *might* be a result of how these different algorithms are benchmarked, but yes, that really looks a bit odd, especially since the RAID6 code *also* computes the XOR checksum (it does P and Q in parallel since it has to read the data anyway). -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
