em(4) high latency w/o msix

[Hooman Fazaeli]

8.2-RELEASE and stable/8 have the same problem. Ping RTT triples
when MSIX is disabled.

On 10/3/2011 11:50 AM, Jack Vogel wrote:
> Can you try the driver in 8.2 and possibly stable/8 to see the behavior there.
>
> And, just curious, why are you disabling MSIX?
>
> Jack
>
>
> On Mon, Oct 3, 2011 at 12:51 AM, Hooman Fazaeli <fazaeli at sepehrs.com <mailto:fazaeli at sepehrs.com>> wrote:
>
>     Hi Jack
>
>     The hardware is a PCIe network appliance with 3 port modules. The ports I have
>     used in the test are 82574L residing on a 4 port module. Anyway, as I noted
>     in last mail, the stock 7.3-RELEASE driver does not expose this problem on
>     the same hardware.
>
>
>     On 10/2/2011 7:38 PM, Jack Vogel wrote:
>>     On what hardware?
>>
>>     Jack
>>
>>
>>     On Sun, Oct 2, 2011 at 6:42 AM, Hooman Fazaeli <fazaeli at sepehrs.com <mailto: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 <http://192.168.1.83>: icmp_seq=0 ttl=64 time=0.055 ms
>>         64 bytes from 192.168.1.83 <http://192.168.1.83>: icmp_seq=1 ttl=64 time=0.076 ms
>>         64 bytes from 192.168.1.83 <http://192.168.1.83>: icmp_seq=2 ttl=64 time=0.066 ms
>>         64 bytes from 192.168.1.83 <http://192.168.1.83>: icmp_seq=3 ttl=64 time=0.051 ms
>>         64 bytes from 192.168.1.83 <http://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 <http://192.168.1.83>: icmp_seq=0 ttl=64 time=0.180 ms
>>         64 bytes from 192.168.1.83 <http://192.168.1.83>: icmp_seq=1 ttl=64 time=0.164 ms
>>         64 bytes from 192.168.1.83 <http://192.168.1.83>: icmp_seq=2 ttl=64 time=0.169 ms
>>         64 bytes from 192.168.1.83 <http://192.168.1.83>: icmp_seq=3 ttl=64 time=0.172 ms
>>         64 bytes from 192.168.1.83 <http://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?
>>
>>
>>
>>
>>
>