On Fri, 19 Nov 2021 at 10:49, james list <[email protected]> wrote:
Hey, > I try to rephrase the question you do not understand: if I enable cut through > or change buffer is it traffic affecting ? There is no cut-through and I was hoping after reading the previous email, you'd understand why it won't help you at all nor is it desirable. Changing QoS config may be traffic affecting, but you likely do not have the monitoring capability to observe it. > Regarding the drops here the outputs (15h after clear statistics): You talked about MX, so I answered from MX perspective. But your output is not from MX. The device you actually show has exceedingly tiny buffers and is not meant for Internet WAN use, that is, it does not expect significantly higher sender rate to receiver rate with high RTT. It is meant for datacenter use, where RTT is low and speed delta is small. In real life Internet you need larger buffers because of this senderPC => internets => receiverPC Let's imagine an RTT of 200ms and receiver 10GE and sender 100GE. - 10Gbps * 200ms = 250MB TCP window needed to fill it - as TCP windows grow exponentially in absence of loss, you could have 128MB => 250MB growth - this means, senderPC might serialise 128MB of data at 100Gbps - this 128MB you can only send at 10 Gbps rate, rest you have to take into the buffers - intentionally pathological example - 'easy' fix is, that sender doesn't burst the data at its own rate, but does rate estimation and sends window growth at estimated receiver rate, this practically removes buffering needs entirely - 'easy' fix is not standard behaviour, but some cloudyshops configure their linux like this thankfully (Linux already does bandwidth estimation, and you can ask 'tc' to shape the session to esimated bandwidth' What you need to do is change the device to a one that is intended for the application you have. If you can do anything at all, what you can do, is ensure that you have minimum amount of QoS classes and those QoS classes have maximum amount of buffer. So that unused queues aren't holding empty memory while used queue is starving. But even this will have only marginal benefit. Cut-through does nothing, because your egress is congested, you can only use cut-through if egress is not congested. -- ++ytti _______________________________________________ juniper-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/juniper-nsp
