Maintained by: NLnet Labs

[Unbound-users] Packets lost when multi threading

W.C.A. Wijngaards
Fri Dec 7 12:38:27 CET 2012


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Hi Leo,

On 12/07/2012 12:20 PM, Leo Baltus wrote:
> Op 07/12/2012 om 11:50:04 +0100, schreef W.C.A. Wijngaards:
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>> 
>> Hi Leo,
>> 
>> On 12/07/2012 11:29 AM, Leo Baltus wrote:
>>> Hi,
>>> 
>>> When I run unbound multi-threaded perf keeps reporting
>>> 'Packets lost', but when it runs single threaded it does not.
>>> 
>>> $ perf -d 10 -a 'www.omroep.nl IN A' 2a02:458:101:31::34 qps: 
>>> 29262.9 qps: 31986.4 qps: 32167.5 qps: 32479.7 qps: 33064.3
>>> qps: 32174.4 qps: 31408.1 qps: 35887.4 qps: 37471.3 qps:
>>> 35364.5 overall time: 	10.0001 sec Packets lost: 	732
>>> 0(NOERROR): 	331249 replies average qps: 	33124.5
>>> 
>>> This is unbound-1.4.18 with openssl-1.0.0j, ldns-1.6.16 and 
>>> libevent-2.0.21-stable running on a linux-2.6.27.59 kernel.
>>> 
>>> It even reports this when perf is run on the host running
>>> unbound.
>>> 
>>> Is this a known issue?
>> 
>> No.  Can you try setting so-rcvbuf higher (4m) ?  It may be lost 
>> simply because it is out of buffers.  There is nothing intrinsic
>> in unbound that makes it drop packets in this setup; it must be
>> the OS.
>> 
> 
> It makes no difference.
> 
> here's the multithreading part of my unbound.conf:
> 
> num-threads: 4 outgoing-range: 8192 num-queries-per-thread: 4096 
> so-rcvbuf: 4m
> 
> Also 'netstat -su' does not report any increments on 'receive
> errors' or RcvbufErrors.

Perhaps perf fails to count them?  They may still be in transit, and
perf stops abruptly, counts them as lost?  tcpdump may be able to
count the number of packets that transited and where those 732 packets
went?

Best regards,
   Wouter


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