polling's future [was: Re: Dynamic Ticks/HZ]

Luigi Rizzo rizzo at iet.unipi.it
Tue Nov 6 11:09:15 UTC 2012

On Tue, Nov 06, 2012 at 11:23:34AM +0100, Andre Oppermann wrote:
> Hi Luigi,
> do you agree on polling having outlived its usefulness in the light
> of interrupt moderating NIC's and SMP complications/disadvantages?

yes, we should let it rest in peace.

One part of the NIC-polling framework is now obsoleted by the
interrupt moderation that most NICs support (note though that
almost none of the popular hypervisors emulate interrupt moderation
so your network performance in a VM will be awful under heavy load.)

Unfortunately another part will be lost even on bare hardware:
NIC-polling, as implemented in FreeBSD, had the ability to cap the
amount of CPU time spent in the polling loop during each tick, thus
making sure there is no livelock.  Neither taskqueue nor NAPI (in
linux world) have this feature.


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