I still play with 5400s, but I haven't played with "Guaranteed Minimum Bandwidth", which is probably the feature you want.
FIrst, check how many queues you have configured in QoS ("show qos queue-config"). Hopefully you haven't fiddled with this and it is set to its default correspondences.
Then, you assign a bandwidth % for each queue on your outbound "edge" port, eg
int a1-a5 bandwidth-min output 2 3 30 10 10 10 15 20
or
int a1-a5 bandwidth-min output 2 3 30 10 10 10 15 strict
(Queues in order from 1 to 8. "strict" means 8 gets everything it needs. Otherwise if set to "20", 8 gets 20%, plus it gets to use whatever it needs from whatever is unused in all the other queues. Then 7 gets its chance, etc... If your %s don't all add up to 100, then whatever is left over is just unused and available for use by any oversubscribed queues, highest-priority queue getting first choice).
The traffic is assigned a queue according to the 802.1p frame tags.
(HP seem to love using 6 for voice, but normally 802.1p says 5 should be used for voice, I think they've confused TOS 5 with queue 6, or I just haven't understood them properly).
Just looking in the manual, they seem to explain this correctly:
Table 20 Per-port outbound priority queues
802.1p Priority settings in tagged VLAN packets1 Outbound priority queue for a given port
1 (low) 1
2 (low) 2
0 (normal) 3
3 (normal) 4
4 (medium) 5
5 (medium) 6
6 (high) 7
7 (high) 8
This is correct, because you shouldn't be using TOS 6 (which is 110) or 7 (111).
But elsewhere, I swear I see them trying to get you to use TOS 6 for voice instead of 5 (correct value of 101).
Mind you, all that can be moot anyway if your upstream provider haven't got their network configured properly: I have a WAN link where a TOS of 4 is prioritised (good, normally used for video), 0 is given default priority, but a TOS of 5 experiences 50% packet loss. And apparently this large, multinational telecom company doesn't understand what they are doing wrong when I tried explaining it to them. Twice. Their guys in suits didn't believe me that they would be doing this, and their guys in jeans didn't see the problem.