On Mon, 2007-12-03 at 07:12 +0200, Avi Kivity wrote:
quoted text
> Andi Kleen wrote:
> > Avi Kivity <avi@argo.co.il> writes:
> >   
> >> [I really doubt there are that many of these; syscall
> >> entry/dispatch/exit, interrupt dispatch, context switch, what else?]
> >>     
> >
> > Networking, block IO, page fault, ... But only the fast paths in these 
> > cases. A lot of the kernel is slow path code and could probably
> > be written even in an interpreted language without much trouble.
> >
> >   
> 
> Even these (with the exception of the page fault path) are hardly "we 
> care about a single instruction" material suggested above.  Even with a 
> million packets per second per core (does such a setup actually exist?)  
> You have a few thousand cycles per packet.  For block you'd need around 
> 5,000 disks per core to reach such rate

Intel's newest dual 10GbE NIC can easily (?) throw ~14M packets per
second. (theoretical peak at 1514bytes/frame)
Granted, installing such a device on a single CPU/single core machine is
absurd - but even on an 8 core machine (2 x Xeon 53xx/54xx / AMD
Barcelona) it can still generate ~1M packets/s per core.

Now assuming you're doing low-level (passive) filtering of some sort
(frame/packet routing, traffic interception and/or packet analysis)
using hardware assistance (TSO, complete TCP offloading, etc) is off the
table and each and every cycle within netif_receive_skb (and friends)
-counts-.

I don't suggest that the kernel should be (re)designed for such (niche)
applications but on other hand, if it works...

- Gilboa

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