[Asterisk-Users] Opinions on renice or turning off swap or ramdis k as swap?

[Rich Adamson]

For those of us that aren't (and will probably never be) linux performance
experts, would it be possible for those with at least some knowledge to
post some basic how-to's that have proven to helpful in the * environment?

If it makes sense to others, I'd volunteer to accept on-list or off-list
emails, consolidate them, and enter them in the wiki (or even post them
on another site if needed) for the benefit of all. Sure seems to be a
need for this. Direct email to radamson at routers.com if you'd like.

Rich

------------------------
> > I have 4 gig in my * box. I'm tuning for performance and I'd like to ask
> > opinions:
> > 
> > 1. asterisk -p == renice -20 ?? 
> 
> The -p option sets asterisk to realtime priority if possible. This is 
> different from the traditional unix nice levels. A program with realtime 
> priorities will _never_ be preempted by a normal program. A program with 
> the traditional unix nicelevel of -20 will give up some time slots to 
> lower priority programs.
> 
> This has advantages (scheduling of packets are much better e.g.) and 
> disadvantages (a broken asterisk server will leave the system impossible 
> to log in to). The disadvantage can be soften by keeping a shell open with 
> realtime priority (higher) around.
> 
> Running with -p does help a lot for VoIP stuff.
> 
> Note that this is user-space (pseudo) realtime stuff. Lowlatency patches 
> for the kernel can give better response time for the zaptel drivers as 
> well. This is orthogonal.
> 
> > 2. I've turned off swap with no apparent ill effects. Can anyone commment on
> > long term effects with moderate load (say, 30 SIP phones / 2-3K calls /day)
> 
> Turning off swap means that the only page-freeing operation left is demand 
> paging of binaries. I.e. program text pages (the actual program that is) 
> are discarded and reloaded. This can be a rather bad idea.
> 
> Asterisk should stay resident in memory under normal circumstances. There 
> can be a problem if you are running an ide disk and have unmasq irq turned 
> off. In that case disk accesses will definitly hurt you. For any hardware 
> from this side of the millenium unmasq irq should be safe.
> 
> > 3. Can anyone comment on using ramdisk as swap and whether this is a good
> > idea or bad idea?
> 
> That is a bad idea. Use the ram as ram instead.
> 
> > I'm using 2.6 kernel. I've modified the PCI latency in rc.local:
> > 
> > setpci -v -s <my T100P address> latency_timer=ff
> 
> Are you sure that is a good idea? That only makes the T100 hold the bus 
> longer. If my memory serves me the T100P is not bus mastering. I don't 
> think the pci latency value for it is relevant, but I am not sure. I do 
> believe the latency values of the other devices is at least as important. 
> The T100P does not need to transfer many bytes at a time, but it does need 
> to transfer them as soon as possible when they are ready.
> 
> Peter
> 
> 
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