Thanks for the quick response (as always) Mike. Ok. I see where you're going. I should be able to build a kernel, but I have already veered a little bit away from where Oracle already is with their OVM kernel. I don't want to veer to far (even with printk statements)-- but maybe... let me think about possibly doing something with just tcpdump to see if I can see tcp windows scaling real low.
We have a concern at ITEC that the EqualLogic is setting TCP windows towards zero. And when it does that we are concerned that if it does this too much, even noop pings aren't getting through. So... let think about this and see if I can respond again to you tomorrow morning. Thanks again for jumping on this. Joe On Apr 28, 2011, at 6:29 PM, Mike Christie wrote: > On 04/28/2011 02:42 PM, Joe Hoot wrote: >> Mike or others, >> >> I would like to enable a small (yes, feel free to snicker here...) bit of >> debugging on one of our systems to try to capture tcp window sizes (so that >> I can attempt to trend some behaviors). Mike, recall awhile ago you had >> mentioned that the following will help us gather more information: >> > > How are you setting the window sizes? > >> echo 1> /sys/module/libiscsi2/parameters/debug_libiscsi >> echo 1> /sys/module/libiscsi_tcp/parameters/debug_libiscsi_tcp >> echo 1> /sys/module/iscsi_tcp/parameters/debug_iscsi_tcp >> >> I believe that the only one that I really need to turn on to get more >> information about size of data being sent would be this one: >> >> echo 1> /sys/module/libiscsi_tcp/parameters/debug_libiscsi_tcp >> >> as it gives me something like this when I run this command: >> [root@oim61024006 ~]# echo 1> >> /sys/module/libiscsi_tcp/parameters/debug_libiscsi_tcp; sleep 1; dd >> if=/dev/zero >> of=/var/ovs/mount/DCA44DBDD7944327A7945E96BF8F7CCC/joetest.dd.img bs=1K >> count=1; echo 0> /sys/module/libiscsi_tcp/parameters/debug_libiscsi_tcp >> 1+0 records in >> 1+0 records out >> 1024 bytes (1.0 kB) copied, 3.7e-05 seconds, 27.7 MB/s >> [root@oim61024006 ~]# >> >> That produced this in /var/log/messages: >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_task_init >> task deq [itt 0x1c6 imm 0 unsol 0] >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_segment_done >> copied 0 0 size 48 xmit >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_segment_done >> copied 0 48 size 48 xmit >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_segment_done >> total copied 48 total size 48 > > Need libiscsi debugging on, but this looks like it might have been a > iscsi pdus related to scsi READ commands. On the next line we see some > data coming in from the target in response to some command. > > >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_recv_skb in >> 560 bytes >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_recv_skb skb >> deace200 ptr=dd84c800 avail=560 >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_segment_done >> copied 0 0 size 48 recv >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_segment_recv >> copying 48 >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_segment_done >> copied 0 48 size 48 recv >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_segment_done >> total copied 48 total size 48 >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_recv_skb >> segment done >> >> ---> and I'm thinking that this is actually where my dd starts going: >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_hdr_dissect >> opcode 0x25 ahslen 0 datalen 512 > > opcode 25 is a iSCSI SCSI DATA_IN. Basically the target sends data to > the initiator in this type of pdu in response to a read command. Below > we see more data getting read in. > >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_hdr_dissect >> iscsi_tcp_begin_data_in( offset=0, datalen=512) > > so here datalen means that the DATA_IN pdu has 512 bytes of data that we > are going to read in. > >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_recv_skb in >> 512 bytes >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_recv_skb skb >> deace200 ptr=dd84c830 avail=512 >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_segment_done >> copied 0 0 size 512 recv >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_segment_recv >> copying 512 >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_segment_done >> copied 0 512 size 512 recv >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_segment_done >> total copied 512 total size 512 >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_recv_skb >> segment done > > So the above blob just means we got the 512 bytes read in successfully. > >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_hdr_recv_prep >> (digest disabled) >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_recv_skb in 0 >> bytes >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_recv_skb no >> more data avail. Consumed 0 >> --> and this is where it had finished? >> >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_segment_done >> copied 0 0 size 0 xmit >> Apr 28 15:26:07 oim61024006 kernel: connection22:0: iscsi_tcp_segment_done >> total copied 0 total size 0 >> >> I'm assuming that these "size 48 recv" might be some keepalive thing (nop >> pings, dm-multipath readsector 0, etc..)? >> > > Is a iscsi header. In a iscsi packet there is basically a header that > tells us what type of command it is (ping, scsi command, ready to > transfer, login, etc), how much data is going to be transferred in the > data segment after the header, etc. > > For the xmit path you need libiscsi debugging on as well as libiscsi_tcp > to determine what type of iscsi header it is. > > See above for info the packets. > >> 3) "iscsi_tcp_recv_skb in 512 bytes" >> >> skb = send kb's? > > skb is a networking thing. It is just short for "struct sk_buff" which > just represents a buffer that we could send/recv to/from. > > >> >> etc... >> >> But what I'm really trying to pull out of this information is trying to >> trend how often the initiator is trying to xmit data, but is not allowed to. >> Maybe there is also a way (outside of just tcpdumping... or even with >> tcpdump, with a tweaked filter so I don't get gigs of pcaps) to understand >> what the tcp window size is currently being set to. >> > > There is no nice printk for when sendpage/sendmsg has failed to send > data. In the past logs I could tell it was happening because in the xmit > messages we would repeat messages like this: > > connection7:0: iscsi_tcp_segment_done copied 2592 0 size 4096 xmit > > which comes from here: > > ISCSI_DBG_TCP(tcp_conn->iscsi_conn, "copied %u %u size %u %s\n", > segment->copied, copied, segment->size, > recv ? "recv" : "xmit"); > > And so the first value is how much we have copied so far. The second > values is how much got copied when we just called sendpage/sendmsg and > the last value size is the total amount of data we want to send. > > In the logs you sent it kept repeating the same values and we never saw > the copied values get incremented and we never saw this message > indicating we sent everything. > > /* Do we have more scatterlist entries? */ > ISCSI_DBG_TCP(tcp_conn->iscsi_conn, "total copied %u total size > %u\n", > segment->total_copied, segment->total_size); > > >> I would then try to parse it after the fact to put the data in rrd graphs. >> >> If there are any sites that explain this in more detail, I would happy to >> dig. The only issue I have is that I'm not a programmer... I haven't >> reviewed or coded in C in about 10 years (and even then I was just learning >> it in school). So if the site is too in depth, I may still be asking >> questions... but regardless, I am more than happy to hit the ground running >> and at least do the due diligence of reviewing the info if someone can point >> me in the right direction. >> > > If you can build I kernel I can make this a lot easier. I can just add a > printk to the sendpage/sendmsg call, and so it will be really easy to > pinpoint. > > -- > You received this message because you are subscribed to the Google Groups > "open-iscsi" group. > To post to this group, send email to open-iscsi@googlegroups.com. > To unsubscribe from this group, send email to > open-iscsi+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/open-iscsi?hl=en. > -- You received this message because you are subscribed to the Google Groups "open-iscsi" group. To post to this group, send email to open-iscsi@googlegroups.com. 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