Mmm, I saw the images had gone too :( I have set up to do a gc log next time I run the test and will dig into it. I've been using the default Java8 GC, which is Parallel, so I am going to use CMS to see if that makes a difference. I gather it is supposed to favour shorter pauses, so I'll see what happens and post back results.
Cheers Antony > -----Original Message----- > From: Kirk Pepperdine [mailto:[email protected]] > Sent: Monday, 19 March 2018 4:39 PM > To: JMeter Users List <[email protected]> > Subject: Re: Feedback and question re Java memory/GC settings for Jmeter > load generator CPU issue > > Hi, > > The images seem to have been filter out of my email at least. > > Can you collect and post a GC log. Most likely young gen is too small but a gc > log would confirm this. > > Kind regards, > Kirk > > > On Mar 19, 2018, at 3:37 AM, Antony Bowesman > <[email protected]> wrote: > > > > Hi, > > > > I just thought I’d send in some info about a problem I’ve been looking at > recently – with a question of best GC settings > > > > I have a number of JMeter load generators (LG) and I have been seeing > CPU spikes on the boxes during a test. I am monitoring CPU and memory > from within a Java sampler, so have the following charts > > > > 1. First chart shows the request/sec rate (RHS axis) in blue and the > > CPU > max % in yellow (sampled every 5s). The blue vertical lines indicate a drop in > request rate (as recorded by the request finishing and therefore being > logged) an a corresponding spike to ‘catch up’. I note that the spikes always > correspond to a spike in CPU. > > 2. The second shows the spikes appearing to correlate with the > > increase > in committed memory > > 3. The third is after the JVM setting change. Note the behaviour still > occurs in CPU/request rate with a CPU spike in the green circle, but not until > the later stages. (NB: CPU scale is CPU% * 200 to fit on the graph) > > > > This behaviour is the same across all the LGs and happens regardless of the > way the target hosts are reached across the network, so I believe it’s a > JVM/host issue. > > > > The original memory settings were > > > > -Xms1G -Xmx12G -XX:NewSize=1024m -XX:MaxNewSize=4096m > > > > But I changed –Xms12G so that all memory is allocated initially and that > makes a huge change to the behaviour. > > > > However, I still see the CPU spike. Has anyone got some optimum GC > settings they have used that can avoid this? > > > > Thanks > > Antony > > > > > > > > > > > > > > --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
