Re: [time-nuts] sync computer clock ticks
[EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Saturday, 5 January 2008 7:12 AM To: time-nuts@febo.com Subject: Re: [time-nuts] sync computer clock ticks In a message dated 1/4/2008 12:07:29 Pacific Standard Time, [EMAIL PROTECTED] writes: Right, and the performance here is not much better than ntp, at least in the tests that I've done. The jitter is slightly better. Warner Hi Warner, et. al., has anyone done any testing/evaluation of the typical performance the SNTP server built into GPSCon can achieve? bye, Said **Start the year off right. Easy ways to stay in shape. http://body.aol.com/fitness/winter-exercise?NCID=aolcmp0030002489 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] sync computer clock ticks
In a message dated 1/5/2008 02:01:34 Pacific Standard Time, [EMAIL PROTECTED] writes: both of which are set with GPSCon from separate GPSDO Units I get an average error of 1.4 seconds with a standard deviation of 0.18 seconds. One of the computers is a desktop and the other a LAPtop and both running XP. Regards Rex Hi Rex, thanks for the info, an RMS error of 1.4 seconds is not really that great... bye, Said **Start the year off right. Easy ways to stay in shape. http://body.aol.com/fitness/winter-exercise?NCID=aolcmp0030002489 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] sync computer clock ticks
The company i work for makes high performance interconnect solutions for super computers. i'm working on a demo where we're sending data around a ring and i wanted to timestamp all the packets as it hits each node of the ring. the servers could be under some stress when this is running. A microsecond is pretty tight. There is a chicken/egg tangle here. If you know the network is good then you can use that to calibrate your clocks. If you know the clocks are good then you can use that to calculate network delays. What's the round trip time when the network is idle? Would something like the following work? run a calibration step on an idle system run your tests run another calibration step post process the data If the two calibration steps agree, then you can just fixup the offsets. If they differ, you may have to try linear interpolation. -- These are my opinions, not necessarily my employer's. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] sync computer clock ticks
Michael Di Domenico wrote: I've used NTP for years, but i was under the impression that it is not able to synchonize the clocks below 1 or 2 seconds. Can you point me towards a specific article that speaks about the configuration parameters to get ntp sync'd that low? Hi Michael -- PC hardware and operating systems can put some limits on NTP performance, though with some attention to detail getting ~1 microsecond with an attached hardware reference clock is fairly straightforward. On a lightly loaded LAN, machines can be sync'd to a server on the same LAN to a few hundred microseconds. Challenges may be (a) in the Windows world, earlier versions (prior to some SP level of XP) have inherent limitations on timekeeping accuracy, and (b) Linux does not directly support high accuracy timekeeping with hardware clocks that provide a PPS signal. For various (mainly political, it seems) reasons you need to do a kernel patch to enable use of the PPS signal. I have a bunch of statistics showing NTP performance at http://www.febo.com/time-freq/ntp/stats/index.html. There, you can see how a group of very high performance stratum 1 servers (with directly connected reference clocks) look across the local LAN, as well as how some local stratum 2 and external stratum 2 servers look. There's also a link there to a page that describes what is probably the most accurate hardware available for an NTP server (and which costs less than $300 to implement). John ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] sync computer clock ticks
Michael: What NTP software are you using? Many are intended just to keep the clock within a second, and don't work very hard at it. The best is to get a port of the real NTP from the source at http://www.ntp.org/ They have ports for most major OS's. You should be able to maintain better than 10 milliseconds to UTC once it has settled for a while. Also be sure to check out the NTP server pool project at http://www.pool.ntp.org/. It's an effort to spread out the load on major NTP servers. Keith Keith Payea Bryant Labs [EMAIL PROTECTED] www.bryantlabs.net (707) 566-8935 -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Michael Di Domenico Sent: Friday, January 04, 2008 6:00 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] sync computer clock ticks I've used NTP for years, but i was under the impression that it is not able to synchonize the clocks below 1 or 2 seconds. Can you point me towards a specific article that speaks about the configuration parameters to get ntp sync'd that low? On Jan 3, 2008 10:25 PM, Bruce Griffiths [EMAIL PROTECTED] wrote: Michael Di Domenico wrote: This has probably been asked many times before, but i am unable to find any documentation to point me in the right direction. And yes i am a newbie with clocks... I'd like to synchronize the clock ticks on 16 different computers running linux, down to the 1usec area. Is this even possible from a computer hardware standpoint? If so, can someone point me towards some documentation that explains how to wire up 16 computers to a reference clock source and override the computer internal clocks? I found the Symetricom website, but it seems light on details on exactly how a solution like this all connects together and they're products are likely outside my budget. Ideally, I'd like to use the serial port on each of these 16 servers to connect to some device to get the synchronization signal from a reference. Even if this was possible, i don't think it would get me to 1usec though. Thanks - Michael Michael Google ntp. It is unlikely that you will synchronise the computer clocks to within 1us with ntp unless the computer hardware and operating system is suitably modified. This can be done cheaply (one machine needs to be setup as a dedicated stratum 1 ntp server synchronised to a good time source like a M12M gps timing receiver or equivalent device). NTP broadcasts the required info as LAN packets. If you really need that precisionyou may need to use ptp with suitable hardware (National Instruments and others have suitable boards) NIST has a webpage on PTP. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] sync computer clock ticks
In message: [EMAIL PROTECTED] Michael Di Domenico [EMAIL PROTECTED] writes: : I've used NTP for years, but i was under the impression that it is not : able to synchonize the clocks below 1 or 2 seconds. Can you point me : towards a specific article that speaks about the configuration : parameters to get ntp sync'd that low? I don't know about other people, but out of the box I get sub 20ms synchronization. Right now, it is sitting at about 12.5ms: remote refid st t when poll reach delay offset jitter == *x.yy.co 10.7.1.1 2 u 965 1024 377 64.176 -12.570 0.508 My config file is just a simple: server 1.2.3.4 # x.yyy.com driftfile /mod/etc/ntp.drift restrict default notrust nomodify restrict 127.0.0.1 restrict 1.2.3.4 restrict 10.0.0.6 restrict 10.0.0.0 mask 255.255.0.0 notrust ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] sync computer clock ticks
In message: [EMAIL PROTECTED] michael taylor [EMAIL PROTECTED] writes: : On Jan 4, 2008 12:03 PM, M. Warner Losh [EMAIL PROTECTED] wrote: : : I don't know about other people, but out of the box I get sub 20ms : synchronization. Right now, it is sitting at about 12.5ms: : : remote refid st t when poll reach delay offset jitter : == : *x.yy.co 10.7.1.1 2 u 965 1024 377 64.176 -12.570 0.508 : : : That's a 12 ms offset from UTC, as far as I understand the original : poster only needs = 1 microsecond synchronization on his local : network. I have no experience with gige networks, but the best I've been able to do on 100baseT networks is 50us. I'm unsure what 1us synchronization really means, since that's starting to get below the level of system calls on fast machines. Warner ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] sync computer clock ticks
I forgot two things! (1) It's all Linux, with stock kernel.org kernels, see below. (2) see comment about the application below. Christian Vogel schrieb: at work, I use it to sync all servers and workstations to 4 stratum 1 NTP-servers. I get ~100us offset usually. Without special hardware I'd say that 1usec is not possible. Server, Gig-Ethernet, 4 hops (=Gigabit) to ntp: *ntp2-rz.rrze.un .GPS. 1 u 758 1024 377 1.225 **-0.179** 0.068 (HP DL380-G3, Dual 3.2 GHz P4, no powersaving) - Temperature fluctuates +/- 3 Deg-Celsius every 20sec due to HVAC Kernel 2.6.21.3 SMP Client, 100Mbit, 5 hops (last 4 are better than Gigabit): *ntp2-rz.rrze.un .GPS. 1 u 987 1024 377 1.577 **-0.111** 0.091 (P4-Celeron, 2.4 GHz, currently throttled to 300 MHz) - Temperature currently stable and possibly very cool, have not been in my office for a week :-) Kernel 2.6.22.1 PREEMP And: We should not forget the original poster's question about if 1 usec precision can be achieved? I'd say that the most important thing about this question is, what application the precision is needed for. For example, do you want to timestamp interrupts to synchronize machinery? Or just note down the timestamps of bittorrent downloads very precisely? Just synchronizing an otherwise idling computer is probably much easier than a machine that is doing a lot of additional work that can mess up the timekeeping by clogging the processor or just creating varying stress on the power-supply lines. Scatterbrained, Chris ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] sync computer clock ticks
In message: [EMAIL PROTECTED] Christian Vogel [EMAIL PROTECTED] writes: : For example, do you want to timestamp interrupts to synchronize : machinery? Or just note down the timestamps of bittorrent downloads very : precisely? Just synchronizing an otherwise idling computer is probably : much easier than a machine that is doing a lot of additional work that : can mess up the timekeeping by clogging the processor or just creating : varying stress on the power-supply lines. That's the real question. Like I said before, when you are down to the microsecond level, what good is that? The jitter from system calls and such is going to be high enough to make that not completely useful. And if you are trying to do things to hardware with software that requires that level of synchronization, you aren't going to get it without timestamping done in hardware of some mutually observable event (pps, packets on the network, etc). Warner ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] sync computer clock ticks
Hi Michael, I've used NTP for years, but i was under the impression that it is not able to synchonize the clocks below 1 or 2 seconds. Can you point me towards a specific article that speaks about the configuration parameters to get ntp sync'd that low? at work, I use it to sync all servers and workstations to 4 stratum 1 NTP-servers. I get ~100us offset usually. Without special hardware I'd say that 1usec is not possible. Server, Gig-Ethernet, 4 hops (=Gigabit) to ntp: *ntp2-rz.rrze.un .GPS. 1 u 758 1024 377 1.225 **-0.179** 0.068 (HP DL380-G3, Dual 3.2 GHz P4, no powersaving) - Temperature fluctuates +/- 3 Deg-Celsius every 20sec due to HVAC Client, 100Mbit, 5 hops (last 4 are better than Gigabit): *ntp2-rz.rrze.un .GPS. 1 u 987 1024 377 1.577 **-0.111** 0.091 (P4-Celeron, 2.4 GHz, currently throttled to 300 MHz) - Temperature currently stable and possibly very cool, have not been in my office for a week :-) My main problem is probably that ntp switches between three equally good servers quite frequently (it just did). Chris ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] sync computer clock ticks
M. Warner Losh wrote: In message: [EMAIL PROTECTED] Christian Vogel [EMAIL PROTECTED] writes: : For example, do you want to timestamp interrupts to synchronize : machinery? Or just note down the timestamps of bittorrent downloads very : precisely? Just synchronizing an otherwise idling computer is probably : much easier than a machine that is doing a lot of additional work that : can mess up the timekeeping by clogging the processor or just creating : varying stress on the power-supply lines. That's the real question. Like I said before, when you are down to the microsecond level, what good is that? The jitter from system calls and such is going to be high enough to make that not completely useful. And if you are trying to do things to hardware with software that requires that level of synchronization, you aren't going to get it without timestamping done in hardware of some mutually observable event (pps, packets on the network, etc). Warner PTP achieves submicrosecond synchronisation over small LANs without network switches. It uses hardware time stamping of LAN packets. Someone has even implemented it in software (with degraded performance). See: http://ieee1588.nist.gov/ Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] sync computer clock ticks
In message: [EMAIL PROTECTED] Bruce Griffiths [EMAIL PROTECTED] writes: : M. Warner Losh wrote: : In message: [EMAIL PROTECTED] : Christian Vogel [EMAIL PROTECTED] writes: : : For example, do you want to timestamp interrupts to synchronize : : machinery? Or just note down the timestamps of bittorrent downloads very : : precisely? Just synchronizing an otherwise idling computer is probably : : much easier than a machine that is doing a lot of additional work that : : can mess up the timekeeping by clogging the processor or just creating : : varying stress on the power-supply lines. : : That's the real question. Like I said before, when you are down to : the microsecond level, what good is that? The jitter from system : calls and such is going to be high enough to make that not completely : useful. And if you are trying to do things to hardware with software : that requires that level of synchronization, you aren't going to get : it without timestamping done in hardware of some mutually observable : event (pps, packets on the network, etc). : : Warner : : PTP achieves submicrosecond synchronisation over small LANs without : network switches. : It uses hardware time stamping of LAN packets. Right. This is hardware time stamping of mutually observable events (the two way time exchange). One can measure down to nanosecond levels with custom hardware with 1588. Sam Stein presented a paper at 2006 PITI that talked about an average of 2.5ns with a standard deviation of 0.9ns in measuring clock differences. : Someone has even implemented it in software (with degraded performance). : See: : http://ieee1588.nist.gov/ Right, and the performance here is not much better than ntp, at least in the tests that I've done. The jitter is slightly better. Warner ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] sync computer clock ticks
In a message dated 1/4/2008 12:07:29 Pacific Standard Time, [EMAIL PROTECTED] writes: Right, and the performance here is not much better than ntp, at least in the tests that I've done. The jitter is slightly better. Warner Hi Warner, et. al., has anyone done any testing/evaluation of the typical performance the SNTP server built into GPSCon can achieve? bye, Said **Start the year off right. Easy ways to stay in shape. http://body.aol.com/fitness/winter-exercise?NCID=aolcmp0030002489 ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] sync computer clock ticks
On Fri, Jan 04, 2008 at 10:28:33AM -0700, M. Warner Losh wrote: In message: [EMAIL PROTECTED] I have no experience with gige networks, but the best I've been able to do on 100baseT networks is 50us. I'm unsure what 1us synchronization really means, since that's starting to get below the level of system calls on fast machines. My experience in the late 90s with syncing Linux was based on using serial port 1 PPS interrupts with custom code in the kernel to optimize the serial port modem interrupt path.Time stamps of this interrupt versus the hardware based microclock (based on an incrementing counter in the CPU) were used to drive the NTP PLL which computed the frequency error and time offset for the kernel PLL. I found the microclock readings of time of day on the 1 PPS were usually within 1 us (there were a few late ones due to interrupt off intervals of course). This was on fairly slow server class hardware (Pentium Pro at 200 MHz). On ethernet I would not expect that level of accuracy due to the inherent CSMA/CD algorithm jitter... plus of course whatever the bridge in the star hub introduces... Obviously once one gets into the microsecond area one gets into the world of software relativity where what one means by time of day depends on where one is looking. What I was using to judge performance was what an interrupt level call to microclock returned... but inside a larger software system this will obviously be skewed by the various calling delays to get to the kernel... -- Dave Emery N1PRE/AE, [EMAIL PROTECTED] DIE Consulting, Weston, Mass 02493 An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now either. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] sync computer clock ticks
For example, do you want to timestamp interrupts to synchronize machinery? Or just note down the timestamps of bittorrent downloads very precisely? Just synchronizing an otherwise idling computer is probably much easier than a machine that is doing a lot of additional work that can mess up the timekeeping by clogging the processor or just creating varying stress on the power-supply lines. The company i work for makes high performance interconnect solutions for super computers. i'm working on a demo where we're sending data around a ring and i wanted to timestamp all the packets as it hits each node of the ring. the servers could be under some stress when this is running. i had a feeling what i wanted to do isn't possible, but i figured i'd ask some experts before i give up. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] sync computer clock ticks
Michael Di Domenico wrote: For example, do you want to timestamp interrupts to synchronize machinery? Or just note down the timestamps of bittorrent downloads very precisely? Just synchronizing an otherwise idling computer is probably much easier than a machine that is doing a lot of additional work that can mess up the timekeeping by clogging the processor or just creating varying stress on the power-supply lines. The company i work for makes high performance interconnect solutions for super computers. i'm working on a demo where we're sending data around a ring and i wanted to timestamp all the packets as it hits each node of the ring. the servers could be under some stress when this is running. i had a feeling what i wanted to do isn't possible, but i figured i'd ask some experts before i give up. Unless you use packet time stamping cards as used in network characterisation. Errors of around 120ns or so are typical, see: http://nistboulder.net/Presentations/FCSEFTF2003(final).pdf http://nistboulder.net/Presentations/FCSEFTF2003%28final%29.pdf Suitable PCI cards are available. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] sync computer clock ticks
This has probably been asked many times before, but i am unable to find any documentation to point me in the right direction. And yes i am a newbie with clocks... I'd like to synchronize the clock ticks on 16 different computers running linux, down to the 1usec area. Is this even possible from a computer hardware standpoint? If so, can someone point me towards some documentation that explains how to wire up 16 computers to a reference clock source and override the computer internal clocks? I found the Symetricom website, but it seems light on details on exactly how a solution like this all connects together and they're products are likely outside my budget. Ideally, I'd like to use the serial port on each of these 16 servers to connect to some device to get the synchronization signal from a reference. Even if this was possible, i don't think it would get me to 1usec though. Thanks - Michael ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] sync computer clock ticks
On Thu, Jan 03, 2008 at 10:14:01PM -0500, Michael Di Domenico wrote: I'd like to synchronize the clock ticks on 16 different computers running linux, down to the 1usec area. Is this even possible from a computer hardware standpoint? Ideally, I'd like to use the serial port on each of these 16 servers to connect to some device to get the synchronization signal from a reference. Even if this was possible, i don't think it would get me to 1usec though. I've had ntp sync of the microsecond/nanosecond time of day counter on Linux in the 1 us area using serial port timing with custom mods to the kernel (years ago, I think this is standard now)... This of course DOES NOT sync the actual clock tick interrupts, it only syncs the microclock stuff... The only way I know to sync clock interrupts is to use a common clock oscillator and even then the actual interrupt times will not be synced... unless one does some hardware modifications to the motherboards But it certainly IS possible to get multiple machines to see the same time of day to with around a microsecond or two... -- Dave Emery N1PRE/AE, [EMAIL PROTECTED] DIE Consulting, Weston, Mass 02493 An empty zombie mind with a forlorn barely readable weatherbeaten 'For Rent' sign still vainly flapping outside on the weed encrusted pole - in celebration of what could have been, but wasn't and is not to be now either. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] sync computer clock ticks
Michael Di Domenico wrote: This has probably been asked many times before, but i am unable to find any documentation to point me in the right direction. And yes i am a newbie with clocks... I'd like to synchronize the clock ticks on 16 different computers running linux, down to the 1usec area. Is this even possible from a computer hardware standpoint? If so, can someone point me towards some documentation that explains how to wire up 16 computers to a reference clock source and override the computer internal clocks? I found the Symetricom website, but it seems light on details on exactly how a solution like this all connects together and they're products are likely outside my budget. Ideally, I'd like to use the serial port on each of these 16 servers to connect to some device to get the synchronization signal from a reference. Even if this was possible, i don't think it would get me to 1usec though. Thanks - Michael Michael Google ntp. It is unlikely that you will synchronise the computer clocks to within 1us with ntp unless the computer hardware and operating system is suitably modified. This can be done cheaply (one machine needs to be setup as a dedicated stratum 1 ntp server synchronised to a good time source like a M12M gps timing receiver or equivalent device). NTP broadcasts the required info as LAN packets. If you really need that precisionyou may need to use ptp with suitable hardware (National Instruments and others have suitable boards) NIST has a webpage on PTP. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
