Hal, newbie question. What use case on the internet would be saturating a Gb link with NTP? Surely, before that, we should be recommending a second server closer to the clients?
Assume a large University campus, with 30000 nodes (5k students, each with a tablet and phone, etc). Assume all nodes (including the IOT coffee maker) run an NTP client. With a poll of 100 secs (to make life easier), that is 3000 pkts/s . I have an ancient Pentium 4, from 2005 or earlier. 4GB RAM, 32-bit. ntp -n -c monlist says 67000 slots. It is in the pool, since 2009 or so. CPU load is 1% on each core, except when I run updates, etc. -- Sanjeev Gupta +65 98551208 http://www.linkedin.com/in/ghane On Wed, Apr 7, 2021 at 12:43 PM Hal Murray via devel <devel@ntpsec.org> wrote: > > There are 4 places that might be the limiting factor. > > 1) The wire might be full > 2) The Ethernet chip might not be able to process packets at full wire > speed. > 3) The kernel's input dispatcher thread might run out of CPU cycles. > 4) The client threads might run out of CPU cycles. > > I don't have a good setup to demonstrate the Ethernet chip being the > limiting > factor. I could probably make one by plugging in a junk card. The > gigabit > chips that come on Dell motherboards are OK. They can get close to full > wire > speed, close enough that I'm missing under 100 bits between packets. > > The other limits are reasonably easy to demo. > > I have a box with an Intel E5-1650v3. It has 6 cores at 3.5 MHz. With > HyperThreading, that's 12 CPUs. > > My standard test setup is an echo server. The kernel SoftIRQ thread gets > one > CPU. The other half of that core is left idle. There is an echo server > thread on each of the other 10 CPUs. > > Measured NTP throughput: > pkts/sec uSec/pkt > 426K 2.3 NTP (simple) 48 bytes > 320K 3.1 NTP + AES 68 bytes > 93K 10.7 NTP + NTS 232 bytes > > The wire limit for NTP+NTS (232 UDP bytes) is 407K packets per second. > That's > 2.5 uSec per packet. With 10 CPUs, we have 25 uSec per packet. We only > need > 11 so this processor chip should be able to keep up with a gigabit link > running at full speed. > > Note that a workstation with 4 cores can probably keep up. That leaves 6 > worker threads so we only get 15 uSec of CPU time for each packet, but > that's > still more than 11. I don't know how much running both CPUs of a core > will > slow things down. We'll have to wait and measure that. > > > -- > These are my opinions. I hate spam. > > > > _______________________________________________ > devel mailing list > devel@ntpsec.org > http://lists.ntpsec.org/mailman/listinfo/devel >
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