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From "Daryn Sharp (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-6680) Avoid locking overhead for NO_LABEL lookups
Date Fri, 02 Jun 2017 22:06:04 GMT

    [ https://issues.apache.org/jira/browse/YARN-6680?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16035505#comment-16035505

Daryn Sharp commented on YARN-6680:

# Maybe it was the same before, I just attacked the top few hot spots in a profile to get
us unblocked.  I think Nathan measured a ~10% performance reduction but it was enough to push
the RM off a cliff.  I overall achieved a 2X performance increase from my patches under this
umbrella so maybe this was low hanging fruit.
# Ah yes.  There are other (unnecessary) RW lock hotspots, but the label manager map uses
locks to protect the concurrent map for essentially making a consistent copy.  A concurrent
map can be iterated w/o CME but isn't guaranteed to visit every entry hence why I think the
locks are there.
# Yes.  The goal is optimize the common case.
# Cloning the resource would be very bad.  Resource object allocation overhead is already
very high.

> Avoid locking overhead for NO_LABEL lookups
> -------------------------------------------
>                 Key: YARN-6680
>                 URL: https://issues.apache.org/jira/browse/YARN-6680
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>          Components: resourcemanager
>    Affects Versions: 2.8.0
>            Reporter: Daryn Sharp
>            Assignee: Daryn Sharp
>         Attachments: YARN-6680.patch
> Labels are managed via a hash that is protected with a read lock.  The lock acquire and
release are each just as expensive as the hash lookup itself - resulting in a 3X slowdown.

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