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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 updated HADOOP-885:
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Attachment: WallClock.java
Of course, we should not be depending on the fact that Thread.sleep() is
accurate. Here is a modified patch, Please review.
Regarding benchmark numbers, I think the comparision that I am doing is fair.
In fact, the design goal is such that the precision really does not matter. In
fact, the earlier commentary in the issue describes that there should really be
no difference whether the precision is 1 second or 5 seconds. The quantity to
measure is the time difference between System.curTime() vs WallClock.gettime().
This is precisely what my measurement shows.
> 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
> Assigned To: dhruba borthakur
> Attachments: 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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