From: Jonathan Rajotte-Julien via lttng-dev <lttng-dev@lists.lttng.org>
To: 熊毓华 <xiongyuhua@zju.edu.cn>
Cc: lttng-dev@lists.lttng.org
Subject: Re: [lttng-dev] Some confusion about cpu usage of the lttng-consumerd process
Date: Fri, 27 Nov 2020 09:05:48 -0500 [thread overview]
Message-ID: <20201127140548.GB3947@joraj-alpa> (raw)
In-Reply-To: <40a80cf.2b99.176086d97b1.Coremail.xiongyuhua@zju.edu.cn>
Hi,
On Fri, Nov 27, 2020 at 02:39:28PM +0800, 熊毓华 via lttng-dev wrote:
> Hi,dear.
>
> I have been using lttng to monitor my server these days,but I found something interesting.
>
> The cpu usage of lttng varies with the number of cpu cores of the server.
Which is a bit expected since more CPU means more "data" source from the point
of view of lttng hence more "work" overall.
>
> On the server, I create a tracing session in live mode, using "lttng create my-session --live".
>
> Then,I Start the babeltrace2 and configure it to connect to the relay daemon,using "--input-format=lttng-live" mode.
>
> I used 5 cloud servers,1core4G 2core8G 4core16G 8core16G 8core16G.
>
> And,the same test script was executed above to provide the same workload.
We would need the test script to have some context here of the workload.
>
> As we all know,lttng has 5 processes,
>
> 1.lttng-runas --daemonize
>
> 2.lttng-runas -k --consumerd-cmd-sock /var/run/lttng/kconsumerd/command --consumerd-err-sock /var/run/lttng/kconsumerd/error --group tracing
Based on this you are performing kernel tracing.
>
> 3.lttng-sessiond --daemonize
>
> 4.lttng-relayd -L tcp://localhost:5344
>
> 5.lttng-consumerd -k --consumerd-cmd-sock /var/run/lttng/kconsumerd/command --consumerd-err-sock /var/run/lttng/kconsumerd/error --group tracing
>
>
> The CPU usage of the first four processes is below 2% on the 5 servers,but the lttng-consumerd process is different.
>
> On 1-core、2-core、4-core servers,the CPU usage of the lttng-consumerd process is below 2%.
How is the cpu usage measured here?
>
> But on two 8-core machines, the cpu usage of the lttng-consumerd process reached 10% or more.
Consumerd is responsible of "fetching" data from the ring buffers and "saving"
it either locally (trace on disk) or remotely (streaming/live session). CPU usage
should be a bit correlated with the event production rate. Did you have a look at the
number of events generated for a similar interval?
> And,the cpu usage of the babeltrace process is not much different,just the cpu usage of the lttng-consumerd process varies with the number of cpu cores of the server.
>
> Why it is like this?How should this phenomenon be analyzed?
>
> Looking forward to your reply.
>
> thanks,
> yuhua
>
> _______________________________________________
> lttng-dev mailing list
> lttng-dev@lists.lttng.org
> https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
--
Jonathan Rajotte-Julien
EfficiOS
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next prev parent reply other threads:[~2020-11-27 14:06 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-27 6:39 [lttng-dev] Some confusion about cpu usage of the lttng-consumerd process 熊毓华 via lttng-dev
2020-11-27 14:05 ` Jonathan Rajotte-Julien via lttng-dev [this message]
2020-11-27 15:32 ` 熊毓华 via lttng-dev
2020-11-27 16:04 ` Jonathan Rajotte-Julien via lttng-dev
2020-11-27 17:11 ` Mathieu Desnoyers via lttng-dev
2020-11-28 6:49 ` 熊毓华 via lttng-dev
2020-11-30 14:24 ` Mathieu Desnoyers via lttng-dev
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