Re: netsnmp_large_fd_set_resize() sucking cycles

On Thu, Oct 16, 2014 at 9:48 PM, Jono Poff <[email protected]>
wrote:

>
> Hi,
>
> I'm investigating excessive cpu usage in some server software on Solaris
> 10.
>
> By prstat, the server process is using 13% (out of 25%, since it is a
> single thread on 4 cores).
>
> By Brendan Gregg's hotuser script (see
> http://www.brendangregg.com/DTrace/hotuser) the function
> netsnmp_large_fd_set_resize() is using up to 80% of that.
>
> By the same script, libnetsnmp.so is using over 80%.
>
> The context of the call is that I'm using snmp_select_info() to
> integrate SNMP into my own event loop which uses select().  (This is
> pretty much as described under "Own custom event loop" at
> http://vincent.bernat.im/en/blog/2012-snmp-event-loop.html)
>
> netsnmp_large_fd_set_resize() is called from snmp_read() and run_alarms().
>
> The app is using net-snmp-5.6.1.1.  Would upgrading the library (not a
> trivial task) improve the situation?
>
> Can anyone suggest what can be done to alleviate this.  64 bit Solaris
> has a fixed FD_SETSIZE of 64k, so what does
> netsnmp_large_fd_set_resize() need to resize that for?  Why does it
> require space for more than 65535 handles?
>

It's spending time resizing from 0 to FD_SETSIZE.  The change at
http://sourceforge.net/p/net-snmp/code/ci/4224cabcb112d0d437f9ca9f4d3430501d1c8750/
should help you.

  Bill

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