From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Thrift Subject: Inconsistent Performance Date: Mon, 29 Jul 2013 15:32:49 +1200 Message-ID: <51F5E261.6050600@networklabs.co.nz> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Sender: linux-bcache-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: linux-bcache-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-bcache@vger.kernel.org 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