Hi Martin, Iperf client really reports the number of bytes accepted by the kernel (as the write call returns that value.) If a write returns a number less than zero it could have been because of ENOBUFS and the number of bytes transmitted per that write request is zero. Since the write is setting the value the iperf application layer code knows how many bytes were accepted and hence transmitted by the kernel. It is the write return value that's used to determine the transmit rate and not the write request value.
Bob -----Original Message----- From: Martin T [mailto:m4rtn...@gmail.com] Sent: Thursday, September 18, 2014 3:53 AM To: marc.herb...@gmail.com Cc: iperf-users@lists.sourceforge.net Subject: Re: [Iperf-users] Iperf client sends out less UDP traffic than determined with "-b" flag Marc, I'm afraid I didn't understand your question.. My question has nothing to do with packet loss on the network. In case of packet loss on the network, you see this in server-report if we speak about UDP mode. I'll try to explain once again what I'm confused about. If I start the Iperf client with "iperf -c 10.10.10.1 -fm -t 600 -i 60 -u -b 500m" command and thus request Iperf to send data with bandwidth of 500Mbps and Iperf client reports me that it has sent data at 120Mbps instead of 500Mbps: [ 3] 0.0-600.0 sec 8602 MBytes 120 Mbits/sec ..then this means that Iperf client somehow had to know that some of the data was either: 1) dropped in the local machine, i.e. Iperf client writes to socket at 500Mbps, but before printing the "[ 3] 0.0-600.0 sec 8602 MBytes 120 Mbits/sec" line, it somehow checks that actually not all of the data written to socket was not transmitted 2) Iperf client didn't send the data at faster rate than 120Mbps because it received some error-signals from kernel and immediately sent out datagrams less frequently There is nothing to do with packet loss on network. regards, Martin On 9/18/14, Marc Herbert <marc.herb...@gmail.com> wrote: > Martin, > > What makes you think iperf counts local packet losses differently from > network packet losses? > > Cheers, > > Marc > > 2014-09-18 8:50 GMT+01:00 Martin T <m4rtn...@gmail.com>: > >> Andrew, >> >> I'll rephrase my question which I asked earlier. If Iperf ignores the >> errors regarding lack of memory in interface buffers, then how does >> the Iperf client know that under those conditions it should make the >> write calls to socket less frequently? For example if I start the >> Iperf client with "iperf -c 10.10.10.1 -fm -t 600 -i 60 -u -b 500m" >> command and thus request Iperf to send data with bandwidth of 500Mbps >> and Iperf client reports me that it has sent data at 120Mbps instead >> of 500Mbps: >> >> [ 3] 0.0-600.0 sec 8602 MBytes 120 Mbits/sec >> >> ..then this means that Iperf client somehow had to know that some of >> the data was dropped or Iperf client didn't send the data at faster >> rate than 120Mbps. >> >> >> thanks, >> Martin >> >> On 9/17/14, Andrew Gallatin <galla...@gmail.com> wrote: >> > Actually, there are probably ways you could tell. But the simplest is >> > to >> > just keep re-sending until you don't get an error, which is what >> benchmarks >> > do. >> > >> > On Wed, Sep 17, 2014 at 7:53 AM, Andrew Gallatin <galla...@gmail.com> >> > wrote: >> > >> >> There is no way to know. UDP is lossy, after all. >> >> >> >> On Wed, Sep 17, 2014 at 7:47 AM, Martin T <m4rtn...@gmail.com> wrote: >> >> >> >>> Andrew, >> >>> >> >>> if Iperf ignores the errors regarding lack of memory in interface >> >>> buffers, then how does Iperf know that it should send out the >> >>> datagrams less frequently, i.e. write to socket less frequently? >> >>> >> >>> >> >>> thanks, >> >>> Martin >> >>> >> >>> >> >>> On 9/17/14, Andrew Gallatin <galla...@gmail.com> wrote: >> >>> > In my (cursory) read of the 3.x code, it looked like it >> >>> > ignores NET_SOFTERROR returns & retries. It would be nice if it >> >>> reported >> >>> > the amount of ENOBUF errors it received like netperf does.. >> >>> > >> >>> > On Wed, Sep 17, 2014 at 4:09 AM, Martin T <m4rtn...@gmail.com> >> wrote: >> >>> > >> >>> >> Andrew, Bob, >> >>> >> >> >>> >> did I understand you correctly that while ENOBUFS error code is >> >>> >> not >> >>> >> shown in Iperf client output, the Iperf client actually takes it >> into >> >>> >> account and thus sends data out less frequently? >> >>> >> >> >>> >> >> >>> >> regards, >> >>> >> Martin >> >>> >> >> >>> >> On 9/11/14, Bob (Robert) McMahon <rmcma...@broadcom.com> wrote: >> >>> >> > I thought I remembered hitting the ENOBUFs which is the case per >> >>> >> > the >> >>> >> > source. >> >>> >> > >> >>> >> > // perform write >> >>> >> > currLen = write( mSettings->mSock, mBuf, mSettings->mBufLen ); >> >>> >> > if ( currLen < 0 && errno != ENOBUFS ) { >> >>> >> > WARN_errno( currLen < 0, "write2" ); >> >>> >> > break; >> >>> >> > } >> >>> >> > // report packets >> >>> >> > reportstruct->packetLen = currLen; >> >>> >> > ReportPacket( mSettings->reporthdr, reportstruct ); >> >>> >> > >> >>> >> > A minor nit, the currLen may need to set to zero when >> >>> >> > errno==ENOBUFFS >> >>> >> before >> >>> >> > the ReportPacket() >> >>> >> > >> >>> >> > Also, ione could count the number of writes that return ENOBUFFS >> >>> >> > but >> >>> >> > not >> >>> >> > sure why that's interesting. >> >>> >> > >> >>> >> > As an FYI, I have a tool that manages multiple, distributed >> >>> >> > iperf >> >>> >> sessions >> >>> >> > which I use for wi-fi testing. The following shows an 802.11 >> >>> >> > AC >> >>> wi-fi >> >>> >> link >> >>> >> > that maxes out around 800Mbs. The offered load is 2G and the >> iperf >> >>> >> client >> >>> >> > seems to be reporting properly and responding as expected when >> >>> >> > RF >> >>> >> > attenuation is added and then removed. >> >>> >> > >> >>> >> > utf> udp start; udp linkcheck -now; L1 attn 65; UTF::Sleep 0.3; >> L1 >> >>> >> > attn >> >>> >> 0; >> >>> >> > UTF::Sleep 0.3; udp stop >> >>> >> > 20:45:08 LOG sfast-lx2 iperf -s -w 7350000 -l 1470 -u -i >> >>> >> > 0.1 >> >>> >> > -fb >> >>> >> > -p >> >>> >> > 60001 >> >>> >> > 20:45:08 HNDLR_ udp-rx Server listening on UDP port 60001 >> >>> >> > (sflx2,file12) >> >>> >> > 20:45:08 HNDLR_ udp-rx Receiving 1470 byte datagrams >> >>> >> > (sflx2,file12) >> >>> >> > 20:45:08 HNDLR_ udp-rx UDP buffer size: 8388608 Byte >> (WARNING: >> >>> >> > requested 7350000 Byte) (sflx2,file12) >> >>> >> > 20:45:08 LOG itx-lx1 iperf -c 192.168.1.42 -w 367500 -l >> >>> >> > 1470 >> >>> >> > -u >> >>> >> > -b >> >>> >> 2G >> >>> >> > -B 192.168.1.100 -i 0.1 -fb -S 0x0 -T 255 -t 5356800 -p 60001 >> >>> >> > 20:45:08 HNDLR udp-tx >> >>> >> > ------------------------------------------------------------ >> >>> >> > (43602lx1,file13) >> >>> >> > 20:45:08 HNDLR_ udp-rx [ 3] local 192.168.1.42 port 60001 >> >>> >> > connected >> >>> >> > with 192.168.1.100 port 60001 (sflx2,file12) >> >>> >> > 20:45:08 HNDLR udp-tx Client connecting to 192.168.1.42, >> >>> >> > UDP >> >>> port >> >>> >> 60001 >> >>> >> > (43602lx1,file13) >> >>> >> > 20:45:08 INFO udp-tx TX start: protocol=UDP Offered >> >>> >> > rate=2G >> >>> >> > pktsize=1470 delay=5us >> >>> >> > 20:45:08 HNDLR udp-tx Binding to local address >> >>> >> > 192.168.1.100 >> >>> >> > (43602lx1,file13) >> >>> >> > 20:45:08 HNDLR udp-tx Sending 1470 byte datagrams >> >>> >> > (43602lx1,file13) >> >>> >> > 20:45:08 HNDLR udp-tx UDP buffer size: 735000 Byte >> >>> >> > (WARNING: >> >>> >> requested >> >>> >> > 367500 Byte) (43602lx1,file13) >> >>> >> > 20:45:08 HNDLR udp-tx >> >>> >> > ------------------------------------------------------------ >> >>> >> > (43602lx1,file13) >> >>> >> > 20:45:08 HNDLR udp-tx [ 3] local 192.168.1.100 port 60001 >> >>> >> > connected >> >>> >> > with 192.168.1.42 port 60001 (43602lx1,file13) >> >>> >> > 20:45:08 HNDLR udp-tx [ ID] Interval Transfer >> >>> Bandwidth >> >>> >> > (43602lx1,file13) >> >>> >> > 20:45:08 HNDLR udp-tx [ 3] 0.000-0.100 sec 11244030 Bytes >> >>> >> 899522400 >> >>> >> > bits/sec (43602lx1,file13) >> >>> >> > 20:45:08 LOG L1 attn 65 >> >>> >> > 20:45:08 INFO ::AF-A Setting attn to 65 >> >>> >> > 20:45:08 INFO Sleep 0.3 sec >> >>> >> > 20:45:08 LOG itx-lx1 wl0.0: wlc_send_bar: seq 0x17f tid 0 >> >>> >> > 20:45:08 LOG itx-lx1 wl0.0: wlc_send_bar: seq 0x17f tid 0 >> >>> >> (repeated 1 >> >>> >> > times) >> >>> >> > 20:45:08 LOG L1 attn 0 >> >>> >> > 20:45:08 INFO ::AF-A Setting attn to 0 >> >>> >> > 20:45:08 INFO Sleep 0.3 sec >> >>> >> > 20:45:08 HNDLR udp-tx [ 3] 0.100-0.200 sec 2625420 Bytes >> >>> >> 210033600 >> >>> >> > bits/sec (43602lx1,file13) >> >>> >> > 20:45:08 HNDLR udp-tx [ 3] 0.200-0.300 sec 0.00 Bytes >> >>> >> > 0.00 >> >>> >> bits/sec >> >>> >> > (43602lx1,file13) >> >>> >> > 20:45:08 HNDLR udp-tx [ 3] 0.300-0.400 sec 0.00 Bytes >> >>> >> > 0.00 >> >>> >> bits/sec >> >>> >> > (43602lx1,file13) >> >>> >> > 20:45:08 HNDLR udp-tx [ 3] 0.400-0.500 sec 6251910 Bytes >> >>> >> 500152800 >> >>> >> > bits/sec (43602lx1,file13) >> >>> >> > 20:45:08 HNDLR udp-tx [ 3] 0.500-0.600 sec 10406130 Bytes >> >>> >> 832490400 >> >>> >> > bits/sec (43602lx1,file13) >> >>> >> > 20:45:08 HNDLR udp-tx [ 3] 0.600-0.700 sec 10229730 Bytes >> >>> >> 818378400 >> >>> >> > bits/sec (43602lx1,file13) >> >>> >> > 20:45:08 INFO udp Kill signal -HUP sent to >> >>> (43602lx1,file13) : >> >>> >> > iperf -c 192.168.1.42 -w 367500 -l 1470 -u -b 2G -B >> >>> >> > 192.168.1.100 >> >>> >> > -i >> >>> >> > 0.1 >> >>> >> > -fb -S 0x0 -T 255 -t 5356800 -p 60001 >> >>> >> > 20:45:09 INFO udp Kill signal -HUP sent to >> >>> >> > (sflx2,file12) >> >>> >> > : >> >>> >> iperf >> >>> >> > -s -w 7350000 -l 1470 -u -i 0.1 -fb -p 60001 >> >>> >> > 20:45:09 HNDLR udp-tx Close actions for event handler >> >>> >> > (43602lx1,file13) >> >>> >> > 20:45:09 INFO udp-tx Closed : (43602lx1,file13) >> >>> >> > >> >>> >> > Bob >> >>> >> > -----Original Message----- >> >>> >> > From: Bob (Robert) McMahon >> >>> >> > Sent: Wednesday, September 10, 2014 5:02 PM >> >>> >> > To: Martin T; galla...@gmail.com >> >>> >> > Cc: iperf-users@lists.sourceforge.net >> >>> >> > Subject: RE: [Iperf-users] Iperf client sends out less UDP >> >>> >> > traffic >> >>> than >> >>> >> > determined with "-b" flag >> >>> >> > >> >>> >> > Hi Martin, >> >>> >> > >> >>> >> > Just to confirm Andrew, I'm pretty sure I've seen the write >> syscall >> >>> on >> >>> >> linux >> >>> >> > return ENOBUFFs. I'll check it out in the next few days and let >> >>> >> > you >> >>> >> know. >> >>> >> > >> >>> >> > >> >>> >> > Bob >> >>> >> > -----Original Message----- >> >>> >> > From: Martin T [mailto:m4rtn...@gmail.com] >> >>> >> > Sent: Wednesday, September 10, 2014 5:12 AM >> >>> >> > To: galla...@gmail.com; Bob (Robert) McMahon >> >>> >> > Cc: iperf-users@lists.sourceforge.net >> >>> >> > Subject: Re: [Iperf-users] Iperf client sends out less UDP >> >>> >> > traffic >> >>> than >> >>> >> > determined with "-b" flag >> >>> >> > >> >>> >> > Andrew, Bob: >> >>> >> > >> >>> >> > does Iperf use send() system call? Based on Iperf source code >> >>> >> > and >> >>> >> > tests with strace, it seems to use write() system call to send >> data >> >>> to >> >>> >> > socket and according to write() manual page, it doesn't have a >> >>> similar >> >>> >> > error to ENOBUFS. However, I could easily be wrong here. >> >>> >> > >> >>> >> > >> >>> >> > Andrew, >> >>> >> > >> >>> >> > if Linux kernel silently drops packets in case the device queue >> >>> >> > overflows, then how does Iperf client know that? For example if >> >>> >> > I >> >>> >> > start the Iperf client with "iperf -c 10.10.10.1 -fm -t 600 -i >> >>> >> > 60 >> >>> >> > -u >> >>> >> > -b 500m" command and thus request Iperf to send data with >> bandwidth >> >>> of >> >>> >> > 500Mbps and Iperf client reports me that it has sent data at >> >>> >> > 120Mbps >> >>> >> > instead of 500Mbps: >> >>> >> > >> >>> >> > [ 3] 0.0-600.0 sec 8602 MBytes 120 Mbits/sec >> >>> >> > >> >>> >> > ..then this means that Iperf client somehow had to know that >> >>> >> > some >> >>> >> > of >> >>> >> > the data was dropped or Iperf client was restricted to send data >> at >> >>> >> > faster rate than 120Mbps. How to explain this behavior? >> >>> >> > >> >>> >> > >> >>> >> > thanks, >> >>> >> > Martin >> >>> >> > >> >>> >> > On 9/8/14, Andrew Gallatin <galla...@gmail.com> wrote: >> >>> >> >> No, just that it is fairly new (added 5 years ago in "6ce9e7b >> >>> >> >> ip: >> >>> >> >> Report >> >>> >> >> qdisc packet drops"). Netperf did not have it either, until I >> >>> >> >> tried >> >>> >> >> to >> >>> >> >> figure out why I was getting wildly inaccurate results from >> >>> >> >> netperf >> >>> >> >> (eg, >> >>> >> >> seeing 20Gb/s on a 1GbE link). >> >>> >> >> >> >>> >> >> >> >>> >> >> On Mon, Sep 8, 2014 at 11:34 AM, Bob (Robert) McMahon >> >>> >> >> <rmcma...@broadcom.com >> >>> >> >>> wrote: >> >>> >> >> >> >>> >> >>> Hi Drew, >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> Thanks for the detailed explanation. Do you know any reason >> that >> >>> >> >>> iperf >> >>> >> >>> doesn’t or shouldn’t set IP_RECVERR on the sending socket(s)? >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> Thanks, >> >>> >> >>> >> >>> >> >>> Bob >> >>> >> >>> >> >>> >> >>> *From:* Andrew Gallatin [mailto:galla...@gmail.com] >> >>> >> >>> *Sent:* Monday, September 08, 2014 6:53 AM >> >>> >> >>> *To:* Martin T >> >>> >> >>> *Cc:* iperf-users >> >>> >> >>> *Subject:* Re: [Iperf-users] Iperf client sends out less UDP >> >>> traffic >> >>> >> >>> than >> >>> >> >>> determined with "-b" flag >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> Please, there are no "dropping" or "non dropping" NIC drivers, >> >>> unless >> >>> >> >>> some >> >>> >> >>> driver is so broken that >> >>> >> >>> >> >>> >> >>> it silently returns NETDEV_TX_OK & does not stop its txqueue, >> but >> >>> >> >>> a >> >>> >> >>> driver >> >>> >> >>> that broken would >> >>> >> >>> >> >>> >> >>> not be accepted into the kernel. >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> What is really happening is that the linux kernel is silently >> >>> >> >>> dropping >> >>> >> >>> packets when the device's >> >>> >> >>> >> >>> >> >>> queue is full *AND* when the device queue is too small to hold >> >>> >> >>> the >> >>> >> >>> entire >> >>> >> >>> socket buffer's worth >> >>> >> >>> >> >>> >> >>> of traffic. If you want blocking behavior, you need to ensure >> >>> >> >>> you >> >>> >> >>> have >> >>> >> >>> the driver's queue >> >>> >> >>> >> >>> >> >>> large enough (or the socket buffer small enough) so that the >> >>> driver's >> >>> >> >>> queue can hold an >> >>> >> >>> >> >>> >> >>> entire socket buffer worth of traffic (* the number of active >> >>> sockets >> >>> >> >>> per >> >>> >> >>> queue). You can change >> >>> >> >>> >> >>> >> >>> the driver's queue size via ifconfig txqueuelen. It might be >> >>> better >> >>> >> >>> to >> >>> >> >>> reduce the socketbuffer >> >>> >> >>> >> >>> >> >>> size (and remember that linux multiplies whatever value you >> >>> >> >>> give >> >>> >> >>> it >> >>> >> >>> by >> >>> >> >>> 2, >> >>> >> >>> to account for >> >>> >> >>> >> >>> >> >>> slop...). >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> Note that any silent drops are done by the kernel, not the NIC >> >>> >> >>> and >> >>> >> >>> that >> >>> >> >>> this is >> >>> >> >>> >> >>> >> >>> (bizarrely) the expected behavior on linux. If you don't >> believe >> >>> me, >> >>> >> >>> read the send(2) man page on linux: >> >>> >> >>> >> >>> >> >>> ENOBUFS >> >>> >> >>> >> >>> >> >>> The output queue for a network interface was >> >>> >> >>> full. >> >>> >> >>> This >> >>> >> >>> generally indicates that the >> >>> >> >>> >> >>> >> >>> interface has stopped sending, but may be caused >> by >> >>> >> >>> transient congestion. (Normally, >> >>> >> >>> >> >>> >> >>> this does not occur in Linux. Packets are just >> >>> >> >>> silently >> >>> >> >>> dropped when a device queue >> >>> >> >>> >> >>> >> >>> overflows.) >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> If iperf wants a correct accounting of the packets sent by the >> >>> stack >> >>> >> >>> vs >> >>> >> >>> dropped, iperf must set >> >>> >> >>> >> >>> >> >>> the IP_RECVERR sockopt on the sending socket. This stops the >> >>> kernel >> >>> >> >>> from >> >>> >> >>> silently >> >>> >> >>> >> >>> >> >>> dropping packets, and causes send() to return -ENOBUFS rather >> >>> >> >>> than >> >>> 0 >> >>> >> >>> when >> >>> >> >>> >> >>> >> >>> datagram is dropped due to lack of resources (eg, like BSD >> does). >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> >> >>> Drew >> >>> >> >>> >> >>> >> >> >> >>> >> > >> >>> >> >> >>> > >> >>> >> >> >> >> >> > >> >> >> ------------------------------------------------------------------------------ >> Want excitement? >> Manually upgrade your production database. >> When you want reliability, choose Perforce >> Perforce version control. Predictably reliable. >> >> http://pubads.g.doubleclick.net/gampad/clk?id=157508191&iu=/4140/ostg.clktrk >> _______________________________________________ >> Iperf-users mailing list >> Iperf-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/iperf-users >> > ------------------------------------------------------------------------------ Want excitement? Manually upgrade your production database. When you want reliability, choose Perforce Perforce version control. Predictably reliable. http://pubads.g.doubleclick.net/gampad/clk?id=157508191&iu=/4140/ostg.clktrk _______________________________________________ Iperf-users mailing list Iperf-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/iperf-users ------------------------------------------------------------------------------ Slashdot TV. Video for Nerds. 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