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From "Joshua McKenzie (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-7907) Determine how many network threads we need for native transport
Date Wed, 10 Sep 2014 17:06:33 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7907?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14128732#comment-14128732
] 

Joshua McKenzie commented on CASSANDRA-7907:
--------------------------------------------

I'd want some evidence that pinning to cores is going to give us a measurable benefit before
adding it to the code-base, rather than adding it and leaving it disabled until we can come
up with good defaults for it.  I agree with the conclusion that we likely spend a significant
portion of our cpu time on networking w/in-memory workloads but I'd like to see some quantification
of that before we start writing code to address it. 

Good point on us doing the pinning from within our context - that makes that far more palatable
from an ops perspective.  We don't gain the benefit of true isolation of our processes from
kernel preemption in the scheduler but that tends to be a bigger concern on lower index cores
(from my experience) so that's something we can soft-work around.

> Determine how many network threads we need for native transport
> ---------------------------------------------------------------
>
>                 Key: CASSANDRA-7907
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7907
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Benedict
>            Priority: Minor
>
> With the introduction of CASSANDRA-4718, it is highly likely we can cope with just _one_
network IO thread. We could even try pinning it to a single (optionally configurable) core,
and (also optionally) pin all other threads to a different core, so that we can guarantee
extremely prompt execution (and if pinned to the correct core the OS uses for managing the
network, improve throughput further).
> Testing this out will be challenging, as we need to simulate clients from lots of IPs.
However, it is quite likely this would reduce the percentage of time spent in kernel networking
calls, and the amount of context switching.



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