VMS 7.3-2 Copy slow on Alpha

[Jon Pinkley]

John,

Several things to consider:

More than a single system is involved, so a problem on either end can affect performance. You need to look at both systems' memory.

As Volker said, the NPAG_GENTLE and NPAG_AGGRESSIVE parameters are dynamic and therefore they can be changed without a reboot. However, most of the pool fragmentation due to frequent allocation and deallocation from the variable list will remain until the system is rebooted.

Just rebooting itself will "defragment" the pool, so the problem may no longer exhibit itself for a while (or until you run something that thrashes the pool). The fact that the systems haven't been booted for a long period of time suggests that the pool has had an opportunity to be fragmented, especially if pool reclamation is enabled.

Setting the NPAG_GENTLE and NPAG_AGGRESSIVE parameters to 100 will perhaps require more non-paged pool, but it should reduce the fragmentation of the free space in the pool.

What version of VMS are you running? Later versions have more lookaside lists. I don't know what size packets DECnet V is requesting; if they are larger than the size of the largest lookaside list blocksize, then they must be allocated from the variable list, and that gets expensive when the free pool gets fragmented.

Guessing here. Perhaps by specifying a larger windowsize, more buffers are allocated and then reused without freeing/allocating. So perhaps an optimal solution is a combination of turning off reclamation, and specifying a larger windowsize.

Jon