On 18/10/2014 2:44 a.m., Bill Fenner wrote:
On Thu, Oct 16, 2014 at 9:48 PM, Jono Poff
<jonathan.p...@taitradio.com <mailto:jonathan.p...@taitradio.com>> 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
Awesome thankyou! from 80% of total cpu time in this function down to
0.8% :D
Just a couple more questions (and I haven't fully tested snmp
functionality with the change so there may be more, but) ...
Why doesn't the latest version of the library have this patch?
Why does snmplib recreate the fdset each time? In a single threaded app
at least, couldn't this be a static object?
Cheers and thanks again,
Jono
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