[j-nsp] MX80 clksyncd CPU usage

[Blake Willis]

Greetings listers,

        Following up on this thread from last year, the fix in PR789804 does 
indeed seem to provide relief from the burden of 5% cpu used by clksyncd on 
chassis with built-in timing.  The PR reads "With newer chassis 
(MX80/midRangius) program (MX80-T, MX40-T, MX10-T, MX5-T) H/w is reworked to 
implement SPI reads in h/w and it has significantly reduces clksyncd CPU usage 
to around 1-2% of CPU."  In fact it's around 1% on my MX5-Ts.

        However we also have a bunch of MX80s, and we don't need sync ethernet 
so we didn't drop the extra dollarettes (+$12.5K list) on the "timing" model so 
our MX80s still have clksyncd cruising along at 5% cpu.

        As Saku mentioned, disabling clksyncd can cause the MICs to fail to come 
up, so I implemented a less drastic workaround by renice(8)'ing the process.  
It seems like clksyncd is started up by init(8) after /etc/rc.custom is 
executed, so I just added it in /etc/crontab.sys to run every 6 hours:

# make clksyncd more polite
1       */6       *       *       *       root    ps auxw | grep clksyncd | grep -v grep | awk '{print $2}' | xargs renice 20

crontab.sys is sourced at boot to create the crontab, so it needs to be added to 
the crontab manually the first time (or just renice clksyncd by hand).  It'll 
need to be added to crontab.sys again after a jinstall...

Hope that helps.

 -Blake

---
 Blake Willis
 Network Engineering Consultant
 L33 Networks

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