Re: query cable modem too slow

Hi Fredrik,

Thanks your reply.

2014-01-07 17:26 időpontban Fredrik Björk ezt írta:
> I assume the SNR needs to be calculated at that specific point in 
> time and
> that can take a little while. RX power is probably easier for the 
> modem to
> keep track of internally.

No, reading the SNR oid reply time is ok.
But: Reading the RX pwr oid is too slow.

I tried several oids (from the modem) (like TX PWR, sysDescr, etc..) 
and
every case i get the result in normal reply time, only query the RX pwr 
is significantly slower.. :(

> I tried 100 reads using a bash script:
>
> time for (( i=0 ; i-100 ; i++ )) ; do time snmpget -v2c -c public
> 172.19.11.225 1.3.6.1.2.1.10.127.1.1.4.1.5.3 ; done

> real    0m7.656s
> user    0m3.852s
> sys     0m0.384s
>
> Here, again, SNR takes a lot longer to report:
>
> time for (( i=0 ; i-100 ; i++ )) ; do time snmpget -v2c -c public
> 172.19.11.225 1.3.6.1.2.1.10.127.1.1.1.1.6.3 ; done
>
> real    0m30.375s
> user    0m3.916s
> sys     0m0.400s
>
> This particular modem is a Compal CV6181ES running an old FW image
> 3.0.0.0-GA-01-SH. EPC3212 modems also respond slower whne queried for 
> SNR.
> I guess we have to blame Broadcom for this :)
>
> EPC3212 response times (script as above)
>
> real    0m9.023s
> user    0m3.860s
> sys     0m0.452s
>
> real    1m16.681s
> user    0m3.772s
> sys     0m0.504s

We use mainly Thomson modems, and few Cisco.

> One way to reduce polling time is to send multiple queries at the 
> same
> time and let the script sort out the different answers:
>
> snmpget 172.19.14.195 -v2c -c public 1.3.6.1.2.1.10.127.1.1.1.1.6.3
> 1.3.6.1.2.1.10.127.1.1.4.1.5.3

Yes, i use one query and multiple oid, as you say, but the result is 
the same.

> This way, I managed to get the EPC3212 to respond in 1m15 sec for 
> both
> parameters. This way you save the overhead of asking two questions 
> and the
> modem compiling two answers, but the SNR query is still time 
> consuming.
>
>
> What are you trying to acheive? You might get past the delay by 
> having a
> background program continously read the SNR from the modems and
> adding/updating the data to a database (Postgres/MySQL/...) and just 
> read
> from there whenever you need. That will give you the latest data 
> possible
> at an instant.

I develop a docsis NMS system, and i need this docsis data from every 
modems,
then i save that data to the modem rrd files, and later i show in graf.

So in this time we have ~3500 modems, and i would like max. total 
polling time: ~1.5min.
(no more!)

> /Fredrik

-- 
szpal


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