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Emulated XQ polling timer setting and data overrun

by bernier＠pescadoo.net

[ Summary : File transfers between two simh PDP hang, DECnet reports Data overruns and Response timeouts ] At 2:14 AM +0200 26/5/14, Johnny Billquist wrote: This is a problem inside of DECnet on the simulated host. It gets packets faster than it can process them, so some packets are dropped. Unfortunately DECnet deals very bad with systematic packet loss like this. You get retransmissions, and after a while the retransmission timeout backs off until you have more than a minute between retransmission attempts. Anyway, if you can get simh to throttle the ethernet interface, that might help you. (I don't remember offhand if it do support such functionality.) The service polling timer can be adjusted SET XQ POLL={DEFAULT|4..2500} Set to 100 by default. Changing the polling timer makes a huge difference. Have a look at: http://pastebin.com/AZ1U6bh3 Although it still hangs sometimes, reliability has vastly improved upon the erratic behavior of the beginning. Remember, the completion time was about 3 minutes. We're almost there :) This turns into an interesting challenge : optimize XQ service timer to make overruns the lowest possible. This depends on many factors, among them is the data sink bandwidth. You may have flawless copy to TI:, but it will fail to disk. The terminal is actually throttling the transfer. Disks are faster, and emulated disks are order of magnitude faster than the original ones. Emulation is pushing DECnet to speeds it was never designed for. I'm running here as low as 10 polls/sec. Maybe 50 would be optimal, and what about 500? I need a metrics. And tools. Here, I am using AT. to time a 100. blocks file transfer. Overruns and timeouts still raise slowly, but DECnet recovers happily most of the time. -- Jean-Yves Bernier

11 years, 6 months

Quick RT-11 question

by jhfinedp3k＠compsys.to

>Cory Smelosky wrote: >On Mon, 19 May 2014, Jerome H. Fine wrote: Since you are obviously using either V05.06 or V05.07 Yup. 5.07. It has Mentec branding! (only the last two versions of RT-11 have the RT11ZM Monitor), you can use the VRUN command to support giving LINK all 64 KB of memory. Naturally, you will probably need at least 256 KB of total physical memory on even a PDP-11/23 (to run RT11XM as well as to provide the needed extended memory to provide LINK with the full 64 KB to run in) although 128 KB might do in a pinch depending on which device you use for the system device. Thanks. I'll look in to VRUN. Any good results (or bad) to report? How much physical memory do you have? Jerome Fine

11 years, 6 months

"Dropped by adjacent node" ....

by bqt＠softjar.se

On 2014-05-26 04:17, Johnny Billquist wrote: On 2014-05-26 03:47, Bob Armstrong wrote: Increased it to 32, ... That's probably a good idea, but I don't actually think that's the problem. Like I said, I see this happening with several nodes, all on the bridge QNA - MIM, PONDUS, A5RTR, SGC, etc. Yeah. I checked some more, and I actually only have 18 adjacent nodes at MIM:: so this is definitely not the problem. From my point of view, it only seems to be LEGATO:: that is currently acting like a yo-yo... I would guess that either some packets are lost, or else the packet trip times varies a *lot*. We should investigate more, but it's really getting late for me... Johnny -- Johnny Billquist || "I'm on a bus || on a psychedelic trip email: bqt at softjar.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol

11 years, 6 months

"Dropped by adjacent node" ....

by bqt＠softjar.se

On 2014-05-26 03:47, Bob Armstrong wrote: Increased it to 32, ... That's probably a good idea, but I don't actually think that's the problem. Like I said, I see this happening with several nodes, all on the bridge QNA - MIM, PONDUS, A5RTR, SGC, etc. Yeah. I checked some more, and I actually only have 18 adjacent nodes at MIM:: so this is definitely not the problem. From my point of view, it only seems to be LEGATO:: that is currently acting like a yo-yo... Johnny -- Johnny Billquist || "I'm on a bus || on a psychedelic trip email: bqt at softjar.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol

11 years, 6 months

"Dropped by adjacent node" ....

by bob＠jfcl.com

Increased it to 32, ... That's probably a good idea, but I don't actually think that's the problem. Like I said, I see this happening with several nodes, all on the bridge QNA - MIM, PONDUS, A5RTR, SGC, etc. Bob

11 years, 6 months

Same MAC address on different nodes

by bqt＠softjar.se

On 2014-05-26 02:52, Paul_Koning at Dell.com wrote: On May 24, 2014, at 10:15 AM, Johnny Billquist <bqt at softjar.se> wrote: ... Do I need to spell it out? :-) The hardware address is the address the card have from factory. The physical address is the address the software have programmed the card to have. Since DECnet uses specific addresses, the address is changed from the hardware address, since you do not want/need that when running DECnet. Not necessarily exactly that way. Well, we are talking about old hardware here, Paul... :-) The hardware address is the default physical address. It is supposed to be globally unique (not just unique on each LAN). If you have virtual devices, like in SIMH, chances are you re responsible for this (you re in essence the manufacturer). Pedantically, if you administer MAC addresses, they should be from the locally administered address space, i.e., second bit set in the 1st byte. In practice that doesn t matter, but it avoids conflict with real hardware addresses. Right. But you will be really unlucky if you manage to hit an address that you also happen to have some real hardware using, unless you explicitly sets it so. But even more, once DECnet starts up, it becomes irrelevant again, since DECnet changes the MAC address, and do not even consider retaining the ability to use the original MAC address. DECnet Phase IV uses a physical address it supplies rather than the default. Other protocols (including DECnet Phase V) don t. If your NIC type (or its driver) supports only a single physical address, the physical address changes for all protocols when you turn on DECnet Phase IV. That s why you have to turn on DECnet before LAT. Right. However... if your NIC and driver allow per-protocol physical address, then only DECnet Phase IV uses the aa-00-04-00 address and the others continue to use the hardware address. For such systems, you have to be careful that the hardware address is unique even if DECnet is used. DECnet on neither PDP-11 nor VAX tries any such tricks. They just assume you only will have one hardware address per interface, and sets it to what DECnet thinks it should be, and that's it. I have not checked Alpha, but I suspect it never do such a thing either. And I know that DECnet under Linux also don't play this way (or didn't last I looked). So while you are right that it could do this in theory, it is not done by anything as far as I know, and the additional complexity without any real gains outweight the potential use of such a behavior. Most newer DEC NICs (Tulip and beyond) support multiple physical addresses, as does QNA. UNA and LANCE do not. Whether a particular OS/driver implements that is another matter. simh and other things normally use libpcap, and that do not add extra addresses, but just gets the device into promiscuous mode, and then deals with it in software. Johnny -- Johnny Billquist || "I'm on a bus || on a psychedelic trip email: bqt at softjar.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol

11 years, 6 months

"Dropped by adjacent node" ....

by bqt＠softjar.se

On 2014-05-26 03:06, Bob Armstrong wrote: Do you have a max routers set too low on your machine maybe? We have quite a few routers on the bridge segment. $ NCP SHOW EXEC CHAR ... Max broadcast nonrouters = 512 Max broadcast routers = 128 ... $ NCP TELL MIM SHOW EXEC CHAR ... Max broadcast nonrouters = 64 Max broadcast routers = 20 ... Maybe it's too low on MIM?? The message actually makes it sound like MIM is dropping LEGATO, not the other way around. Could be... In fact you are probably right. Just checked, and MIM have a MAX of 20 right now, which I believe is too low here. Increased it to 32, but I need to reboot for it to take effect... Johnny -- Johnny Billquist || "I'm on a bus || on a psychedelic trip email: bqt at softjar.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol

11 years, 6 months

"Dropped by adjacent node" ....

by bob＠jfcl.com

Do you have a max routers set too low on your machine maybe? We have quite a few routers on the bridge segment. $ NCP SHOW EXEC CHAR ... Max broadcast nonrouters = 512 Max broadcast routers = 128 ... $ NCP TELL MIM SHOW EXEC CHAR ... Max broadcast nonrouters = 64 Max broadcast routers = 20 ... Maybe it's too low on MIM?? The message actually makes it sound like MIM is dropping LEGATO, not the other way around. Bob

11 years, 6 months

Same MAC address on different nodes

by Paul_Koning＠Dell.com

On May 24, 2014, at 10:15 AM, Johnny Billquist <bqt at softjar.se> wrote: ... Do I need to spell it out? :-) The hardware address is the address the card have from factory. The physical address is the address the software have programmed the card to have. Since DECnet uses specific addresses, the address is changed from the hardware address, since you do not want/need that when running DECnet. Not necessarily exactly that way. The hardware address is the default physical address. It is supposed to be globally unique (not just unique on each LAN). If you have virtual devices, like in SIMH, chances are you re responsible for this (you re in essence the manufacturer). Pedantically, if you administer MAC addresses, they should be from the locally administered address space, i.e., second bit set in the 1st byte. In practice that doesn t matter, but it avoids conflict with real hardware addresses. DECnet Phase IV uses a physical address it supplies rather than the default. Other protocols (including DECnet Phase V) don t. If your NIC type (or its driver) supports only a single physical address, the physical address changes for all protocols when you turn on DECnet Phase IV. That s why you have to turn on DECnet before LAT. However... if your NIC and driver allow per-protocol physical address, then only DECnet Phase IV uses the aa-00-04-00 address and the others continue to use the hardware address. For such systems, you have to be careful that the hardware address is unique even if DECnet is used. Most newer DEC NICs (Tulip and beyond) support multiple physical addresses, as does QNA. UNA and LANCE do not. Whether a particular OS/driver implements that is another matter. paul

11 years, 6 months

QNA Data overrun (Was: Same MAC address)

by bernier＠pescadoo.net

At 2:14 AM +0200 26/5/14, Johnny Billquist wrote: Aha. So it is 10.2 that gets timeouts when sending packets to 10.1. So 10.1 are dropping packets. Good. Now, in which direction was the transfer attempted? 10.2 -> 10.1, initiated from 10.1: 10.1>NFT TI:=10.2::SOME.FILE This is a problem inside of DECnet on the simulated host. It gets packets faster than it can process them, so some packets are dropped. Unfortunately DECnet deals very bad with systematic packet loss like this. You get retransmissions, and after a while the retransmission timeout backs off until you have more than a minute between retransmission attempts. I have now to find the reason for the packet loss. Anyway, if you can get simh to throttle the ethernet interface, that might help you. (I don't remember offhand if it do support such functionality.) The service polling timer can be adjusted SET XQ POLL={DEFAULT|4..2500} Set to 100 by default. -- Jean-Yves Bernier

11 years, 6 months

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