EXOS Understanding Buffer Sizes

[Anonymous]

Have been trying to work out the buffering sizes in EXOS on various switches but for the purpose of this query I have been experimenting on an X350.

So when you run either of these commands:

Show port buffer
debug hal show platform packet-buffer ports

You get the following components for ports 1-24 and 25-50, which I have assumed are based on 2 x ASIC’s:

• Total Packet Buffer Size
• Total Shared Buffer Size
• Port x Max Shared Buffer Usage
• QPx: Reserved Buffer

The outputs of the buffer commands are given below based on QoS profiles 1 to 8 being configured, removing one, then running the command again.

The problem I am having is getting the maths to match on what you would expect, so my questions are:

1. Is the total packet buffer size of 786432 the total packet buffer for all the ports or is it per ASIC 1-24 and 25-50?

2. How is the shared buffer size calculated:

2a. You would expect this to be a value remaining minus each of the reserved buffer space allocated to each of the QoS profiles per port, per ASIC.

2b. Whenever a QoS profile is deleted the total shared buffer size increases by 83456 for each ASIC (1-24 and 25-50), which divided by 1920 bytes is equal to 43.5 (Which does not equal all 24 or 49 ports), or divided by 24 is equal to 3477 bytes or divided again which is equal to 1739 (which does not equal 1920 bytes) - if you catch my drift 🙂

3. The max shared buffer usage is the one thing that always balances and if left as default is always 25% of the total shared buffer.Appreciate my understanding of this might be completely wrong but hoping someone can straighten it out.

Packet Buffer Allocation for ports in range 1-24
Total Packet Buffer Size: 786432 bytes, Not Overcommitted
Total Shared Buffer Size: 127488
Port 1 Max Shared Buffer Usage: 31872 bytes
QP1: Reserved Buffer: 1920 bytes
QP2: Reserved Buffer: 1920 bytes
QP3: Reserved Buffer: 1920 bytes
QP4: Reserved Buffer: 1920 bytes
QP5: Reserved Buffer: 1920 bytes
QP6: Reserved Buffer: 1920 bytes
QP8: Reserved Buffer: 1920 bytes

Packet Buffer Allocation for ports in range 1:1-24
Total Packet Buffer Size: 786432 bytes, Not Overcommitted
Total Shared Buffer Size: 210944
Port 1 Max Shared Buffer Usage: 52736 bytes
QP1: Reserved Buffer: 1920 bytes
QP3: Reserved Buffer: 1920 bytes
QP4: Reserved Buffer: 1920 bytes
QP5: Reserved Buffer: 1920 bytes
QP6: Reserved Buffer: 1920 bytes
QP8: Reserved Buffer: 1920 bytes

Packet Buffer Allocation for ports in range 1-24
Total Packet Buffer Size: 786432 bytes, Not Overcommitted
Total Shared Buffer Size: 294400
Port 1 Max Shared Buffer Usage: 73600 bytes
QP1: Reserved Buffer: 1920 bytes
QP3: Reserved Buffer: 1920 bytes
QP5: Reserved Buffer: 1920 bytes
QP6: Reserved Buffer: 1920 bytes
QP8: Reserved Buffer: 1920 bytes

Packet Buffer Allocation for ports in range 1-24
Total Packet Buffer Size: 786432 bytes, Not Overcommitted
Total Shared Buffer Size: 377856
Port 1 Max Shared Buffer Usage: 94464 bytes
QP1: Reserved Buffer: 1920 bytes
QP3: Reserved Buffer: 1920 bytes
QP4: Reserved Buffer: 1920 bytes
QP8: Reserved Buffer: 1920 bytes

Packet Buffer Allocation for ports in range 1-24
Total Packet Buffer Size: 786432 bytes, Not Overcommitted
Total Shared Buffer Size: 461312
Port 1 Max Shared Buffer Usage: 115328 bytes
QP1: Reserved Buffer: 1920 bytes
QP4: Reserved Buffer: 1920 bytes
QP8: Reserved Buffer: 1920 bytes

Packet Buffer Allocation for ports in range 1-24
Total Packet Buffer Size: 786432 bytes, Not Overcommitted
Total Shared Buffer Size: 544768
Port 1 Max Shared Buffer Usage: 136192 bytes
QP1: Reserved Buffer: 1920 bytes
QP8: Reserved Buffer: 1920 bytes

Packet Buffer Allocation for ports in range 25-50
Total Packet Buffer Size: 786432 bytes, Not Overcommitted
Total Shared Buffer Size: 231424
Port 25 Max Shared Buffer Usage: 57856 bytes
QP1: Reserved Buffer: 1920 bytes
QP2: Reserved Buffer: 1920 bytes
QP3: Reserved Buffer: 1920 bytes
QP4: Reserved Buffer: 1920 bytes
QP5: Reserved Buffer: 1920 bytes
QP6: Reserved Buffer: 1920 bytes
QP8: Reserved Buffer: 1920 bytes

Packet Buffer Allocation for ports in range 25-50
Total Packet Buffer Size: 786432 bytes, Not Overcommitted
Total Shared Buffer Size: 300032
Port 25 Max Shared Buffer Usage: 75008 bytes
QP1: Reserved Buffer: 1920 bytes
QP3: Reserved Buffer: 1920 bytes
QP4: Reserved Buffer: 1920 bytes
QP5: Reserved Buffer: 1920 bytes
QP6: Reserved Buffer: 1920 bytes
QP8: Reserved Buffer: 1920 bytes

Packet Buffer Allocation for ports in range 25-50
Total Packet Buffer Size: 786432 bytes, Not Overcommitted
Total Shared Buffer Size: 368640
Port 25 Max Shared Buffer Usage: 92160 bytes
QP1: Reserved Buffer: 1920 bytes
QP3: Reserved Buffer: 1920 bytes
QP5: Reserved Buffer: 1920 bytes
QP6: Reserved Buffer: 1920 bytes
QP8: Reserved Buffer: 1920 bytes

Packet Buffer Allocation for ports in range 25-50
Total Packet Buffer Size: 786432 bytes, Not Overcommitted
Total Shared Buffer Size: 437248
Port 25 Max Shared Buffer Usage: 109312 bytes
QP1: Reserved Buffer: 1920 bytes
QP3: Reserved Buffer: 1920 bytes
QP4: Reserved Buffer: 1920 bytes
QP8: Reserved Buffer: 1920 bytes

Packet Buffer Allocation for ports in range 25-50
Total Packet Buffer Size: 786432 bytes, Not Overcommitted
Total Shared Buffer Size: 505856
Port 25 Max Shared Buffer Usage: 126464 bytes
QP1: Reserved Buffer: 1920 bytes
QP4: Reserved Buffer: 1920 bytes
QP8: Reserved Buffer: 1920 bytes

Packet Buffer Allocation for ports in range 25-50
Total Packet Buffer Size: 786432 bytes, Not Overcommitted
Total Shared Buffer Size: 574464
Port 25 Max Shared Buffer Usage: 143616 bytes
QP1: Reserved Buffer: 1920 bytes
QP8: Reserved Buffer: 1920 bytes

Many thanks in advance

[Stephane_Grosj1]

Can't help, really depends on your network and usage.

[davidj_cogliane]

Any thoughts on a safe range to play with?
Should I try 30% or am I safe to try 40%?

Or do I need to calculate a % that would equal an even packet count as someone suggested in another thread?

Thanks,

[Stephane_Grosj1]

Oh, looks like I forgot to answer to that thread 3 years ago 😕

X440G2 does not support Smart Buffer, so it makes sense to fine tune manually the buffer usage for your need on such platform.

I remember a customer playing with that for broadcast IP TV needs, and it solved their issue (that was even on G1 at that time). So yes, it can help a lot.

[davidj_cogliane]

This was a very interesting read and I think my questions are a lot simpler, though I seem to see similar issues.

X440-G2 with congestion on multiple ports over long periods. I se the max shared buffer usage of 25% and was wondering about the pros and cons of adjusting that to 30-40% to alleviate some of the congestion.

Reading the above I now wonder if that is necessary as I thought I just read the switch adjusts dynamically. If I read that wrong my question remains.

How does everyone feel about adjusting the max buffer usage?
What are some %s people have tried?
Has anyone seen improvement by doing this?