From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steven Pratt Subject: More random write performance data Date: Wed, 08 Apr 2009 16:38:17 -0500 Message-ID: <49DD1949.1060503@austin.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed To: linux-btrfs Return-path: List-ID: Given the anomalies we were seeing on random write workloads, I decided to simplify the test and do single threaded odirect random write. This should eliminate the locking issue as well as any pdflush bursty behavior. What I got was not quite what I expected. The most interesting graph is probably #12, DM write throughput. We see a baseline of ~7MB/sec with spikes every 30 seconds. I assume the spike are meta data related as the io is being done from user space at a steady constant rate. The really odd thing is that for the entire almost 2 hour duration, the amplitude of the spike continues to climb, meaning the amount of meta data need to be flushed to disk is ever increasing. http://btrfs.boxacle.net/repository/raid/longrun/btrfs-longrun-1thread/btrfs1.ffsb.random_writes__threads_0001.09-04-08_13.05.54/analysis/iostat-processed.001/chart.html Looking at graph #8 DM IO/sec, we see that there is even a pattern within the pattern of spikes. It # of IOs in each spike appears to change at each interval and repeats over a set of 7, 30 second intervals. Also, we see that we average 12MB/sec of data written out, for 5MB/sec of benchmark throughput. I have queued up a run without checksums and cow to see how much this overhead is reduced. Steve