This is a multi part question please bear with me.
Background synopsis: A large (on the order of millions) of output queue
drops were causing noticeable breakup of multicast video streams.
I learned that the default egress queue size is 160 starting in
12.2.46SE. I upgraded some lab switches, This helped my situation
immensely.
However output queue drops continued albeit much less frequently.
Question 1:
From an off-list reply to my original question I was told I could
increase the number of queues per interface with this policy-map:
policy-map max-queue
class class-default
queue-limit 544
Naturally I would want to apply to this to every interface, however I am
unsure if this will be detrimental. What I don't know is where queue
space exists: DRAM, a small supply of onboard SRAM?
If I allocate 544 queues to every interface on an ME3400-24TS-A will I
starve other processes for memory (unlikely check my math below)?
If the current default queue size is 160 and I increase it to 544 for
all FastEthernet interfaces I would increase the amount of memory usage
by 2.25 megabytes:
Queue size is 256 bytes; 24 interfaces.
((256*(544-160)bytes))*24 = 2.25 megabytes
Since these ME3400s are just access switches I seem to always at least
50MB of free memory. Therefore 2.25 MBs doesn't seem like a big impact.
Am I correct in my calculations about the impact of the preceding
policy-map applied system wide? Do the output queues live in run of the
mill DRAM?
Question 2:
When I do apply the 'max-queue' policy-map to an interface and inspect
my work:
sh platform qos debug port-class
sh platform qos debug port-config X
Port Class 0: Queue #3 seems to have my new max-queue setting but every
other Port Class and corresponding Queue are still set to 48 (The
pre-12.2.46SE default queue size?)
Am I missing something when I use these commands? This is new territory
for me.
Question 3:
Are the FastEthernet ports on the ME3400 over subscribed in any way? Can
I expect line-rate performance on every port at once or is there an ASIC
handling groups of 2^n ports?
Thanks in advance for any help.
****
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