Re: [GIT PULL] AlacrityVM guest drivers for 2.6.33

From: Chris Wright
Date: Wed Dec 23 2009 - 13:34:57 EST

* Anthony Liguori (anthony@xxxxxxxxxxxxx) wrote:
> The "poor" packet latency of virtio-net is a result of the fact that we
> do software timer based TX mitigation. We do this such that we can
> decrease the number of exits per-packet and increase throughput. We set
> a timer for 250ms and per-packet latency will be at least that much.

Actually that's 150us ;-) It's the AlacrityVM numbers that show 250us
(note micro, not milli) for latency. That makes sense, shave off 150us
for the timer and you're left w/ 100us, which is not substantially
slower than what we see (for that bare metal latency we see ~60us)
when we switched tx mitigation schemes from timer based to thread
scheduling. Quite similar to the 56.8us that vbus/venet shows.

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