Hi,
We are noticing some odd performance characteristics with bcache on 3.10
Mainline kernel.
We are using Intel DC S3700 SSD and Seagate Constellation ES.2 HDD
Using FIO to perform a 4K random write test with QD=32 and 4 instances
we get:
RAW SSD: 55.5K iops
RAW HDD: 540 iops
Fresh bcache on top of SSD/HDD [writeback]: 36.8K iops
Which is not great, but OK.
However if I run the FIO test a number of times, letting it write out
the data to the backing device after each run, after a few runs I will
notice the IOPS drop. When the benchmark starts it will sit around 14K
IOPS, then as soon as it starts writing to the backing device this will
drop to around 5K IOPS. On the subsequent runs it will never go above 5K
IOPS.
Has there been a performance regression on 3.10 ?
Regards,
Andrew
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