Marc,
> In this case, what throughput number do you get on the server side? Different
> from the client or always the same?
Throughput I see on a server side was always the same as Iperf client
reported, e.g. if Iperf client reported "[ 3] 0.0-600.0 sec 8602
MBytes 120 Mbits/sec" then both Iperf server and switches between
the client and server saw 120Mbps of traffic.
> Is 120Mb/s the UDP maximum you ever see on the client, whatever parameters
> you use?
Correct.
> What is the maximum UDP sending rate you ever saw reported on this specific
> hardware and operating system?
It was a VMware virtual-machine(Debian Wheezy was a guest-OS) and
maximum UDP sending rate I received on this particular virtual-machine
was 120Mbps. If I replaced
the guest-OS in this very same virtual-machine with CentOS 7, the same
Iperf release with the same command was able to send traffic at
500Mbps.
Bob,
thank you for this very clear explanation! So for example in those two
write system calls:
[pid 14025]
write(3,"\0\0\0\16T\n\331a\0\3\2563\0\0\0\0\0\0\0\1\0\0\23\211\0\0\0\0\0\17B@"...,1470)
= 1470
[pid 14025] nanosleep({0, 11071000}, <unfinished ...>
[pid 14026] <... nanosleep resumed> NULL) = 0
[pid 14026] nanosleep({0, 10000000}, NULL) = 0
[pid 14026] nanosleep({0, 10000000}, <unfinished ...>
[pid 14025] <... nanosleep resumed> 0xb74ba2c8) = 0
[pid 14025] gettimeofday({1409997153, 252946}, NULL) = 0
[pid 14025]
write(3,"\0\0\0\17T\n\331a\0\3\334\22\0\0\0\0\0\0\0\1\0\0\23\211\0\0\0\0\0\17B@"...,1470)
= 1470
[pid 14025] nanosleep({0, 11088000}, <unfinished ...>
[pid 14026] <... nanosleep resumed> NULL) = 0
[pid 14026] nanosleep({0, 10000000}, <unfinished ...>
[pid 14025] <... nanosleep resumed> 0xb74ba2c8) = 0
[pid 14025] gettimeofday({1409997153, 264721}, NULL) = 0
..the number after the equals sign(1470) is the write return value aka
number of bytes accepted by kernel? And Iperf client just sums those
write() return values together and reports the amount of data
transmitted in bytes and in bps?
I also created a small program in C which writes a string into file
and here is the strace comparison when write() is successful:
open("/media/file.txt", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3
write(3, "Test string\n", 12) = 12
exit_group(12) = ?
..and when the media is full:
open("/media/file.txt", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3
write(3, "Test string\n", 12) = -1 ENOSPC (No space left on device)
exit_group(-1) = ?
regards,
Martin
On Fri, Sep 19, 2014 at 2:58 AM, Marc Herbert <marc.herb...@gmail.com> wrote:
>> 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
>
> Whether packets are lost inside the sender or not and no matter how hard it
> tries, the client cannot perform an infinite number of write() per seconds.
> There is a "physical" limit caused by either the CPU, or memory bandwidth,
> or scheduling, etc. What is the maximum UDP sending rate you ever saw
> reported on this specific hardware and operating system?
>
> As already suggested on this list a few times over the years, also try
> varying the socket buffer size and see if it makes any difference.
>
> Marc
>
> 2014-09-18 11:52 GMT+01:00 Martin T <m4rtn...@gmail.com>:
>>
>> 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
>> >>
>> >
>
>
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