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https://issues.apache.org/jira/browse/HADOOP-885?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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dhruba borthakur resolved HADOOP-885.
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Resolution: Fixed
This issue arose because of the fact that java 1.5 was being used and the
poll() for sockets consumed lots of CPU. The CPU consumption of an idle 900
node cluster came down to 4 to 5% when java 1.6 was used. gettimeofday is
hardly consumes much CPU.
I am closing his JIRA as "Wont-fix".
> Reduce CPU usage on namenode: gettimeofday
> ------------------------------------------
>
> Key: HADOOP-885
> URL: https://issues.apache.org/jira/browse/HADOOP-885
> Project: Hadoop
> Issue Type: Bug
> Components: dfs
> Affects Versions: 0.10.1
> Reporter: dhruba borthakur
> Assignee: dhruba borthakur
> Attachments: gettime1.patch, WallClock.java
>
>
> On a 900 node idle cluster, the namenode spends about 20% of CPU. Most of
> this CPU is spent processing pure heartbeats. No jobs are running on this
> cluster and all nodes are alive and acting well.
> Of the total namenode CPU usage, about 12% is in usermode and about 70% is in
> kernel mode! The question that natually arises is why is heartbeat processing
> taking so much time in kernel mode?
> An strace of namenode reveals that a 20 second period has about 52000
> syscalls with the following breakup:
> gettimeofday : 18000 calls
> accept : 2655 calls
> close : 2655 calls
> shutdown : 2655 calls
> fcntl : 7965 calls
> read : 7965 calls
> futex : 5295 calls
> poll : 4894 calls
> A code inspection reveals that the code is doing multiple (about 5) calls to
> System.currentTimeMillis() in processing a single request in the RPC.java and
> Server.java classes. This might mean that there is a possibility of
> optimization.
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