em(4) high latency w/o msix

[Jack Vogel]

There are differences between adapter and LOM, furthermore, someone could
toggle
the variable on hardware not using it... SO my question stands, I want to
know
hardware details.

Jack


On Sun, Oct 2, 2011 at 5:29 PM, Arnaud Lacombe <lacombar at gmail.com> wrote:

> Hi,
>
> On Sun, Oct 2, 2011 at 12:08 PM, Jack Vogel <jfvogel at gmail.com> wrote:
> > On what hardware?
> >
> Only the 82574 is using em(4)'s MSI-X.
>
>  - Arnaud
>
> > Jack
> >
> >
> > On Sun, Oct 2, 2011 at 6:42 AM, Hooman Fazaeli <fazaeli at sepehrs.com>
> wrote:
> >
> >>
> >> Latest em(4) driver from HEAD seems to have high latency
> >> when MSIX is disabled.
> >>
> >> With MSIX enabled (hw.em.enable_msix=1):
> >>
> >> # ping -c5 192.168.1.83
> >> PING 192.168.1.83 (192.168.1.83): 56 data bytes
> >> 64 bytes from 192.168.1.83: icmp_seq=0 ttl=64 time=0.055 ms
> >> 64 bytes from 192.168.1.83: icmp_seq=1 ttl=64 time=0.076 ms
> >> 64 bytes from 192.168.1.83: icmp_seq=2 ttl=64 time=0.066 ms
> >> 64 bytes from 192.168.1.83: icmp_seq=3 ttl=64 time=0.051 ms
> >> 64 bytes from 192.168.1.83: icmp_seq=4 ttl=64 time=0.063 ms
> >>
> >> --- 192.168.1.83 ping statistics ---
> >> 5 packets transmitted, 5 packets received, 0.0% packet loss
> >> round-trip min/avg/max/stddev = 0.051/0.062/0.076/0.009 ms
> >>
> >> With MSIX disabled:
> >>
> >> # ping -c5 192.168.1.83
> >> PING 192.168.1.83 (192.168.1.83): 56 data bytes
> >> 64 bytes from 192.168.1.83: icmp_seq=0 ttl=64 time=0.180 ms
> >> 64 bytes from 192.168.1.83: icmp_seq=1 ttl=64 time=0.164 ms
> >> 64 bytes from 192.168.1.83: icmp_seq=2 ttl=64 time=0.169 ms
> >> 64 bytes from 192.168.1.83: icmp_seq=3 ttl=64 time=0.172 ms
> >> 64 bytes from 192.168.1.83: icmp_seq=4 ttl=64 time=0.167 ms
> >>
> >> --- 192.168.1.83 ping statistics ---
> >> 5 packets transmitted, 5 packets received, 0.0% packet loss
> >> round-trip min/avg/max/stddev = 0.164/0.170/0.180/0.005 ms
> >>
> >> As you see, w/o MSIX, RTT increases by a factor of 3.
> >>
> >> I also tested the following drivers:
> >>    - igb(4) from HEAD: OK.
> >>    - Stock 7.3-RELEASE: OK.
> >>    - Stock 7.4-RELEASE: problem exist.
> >>
> >> Any ideas?
> >>
> >>
> >>
> >>
> >>
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