Re: [Scst-devel] debug sometimes slow performance

[Bart V. A. <bva...@ac...>]

On 04/28/14 03:56, Vasiliy Tolstov wrote:
> 2014-04-03 20:16 GMT+04:00 Bart Van Assche <bva...@ac...>:
>> Without further information it's hard to tell what's going on. Have you
>> already checked the IB error counters ?
> 
> Bart, can you help - what mean this errors:
> -W- lid=0x002e guid=0x00066a00e3003293 dev=29472 Port=36
>       Performance Monitor counter     : Value
>       vl15_dropped                    : 0x2
> -W- lid=0x0001 guid=0x0008f105001086ac dev=23130 Port=3
>       Performance Monitor counter     : Value
>       port_xmit_discard               : 0x4f
> -W- lid=0x0001 guid=0x0008f105001086ac dev=23130 Port=7
>       Performance Monitor counter     : Value
>       port_xmit_discard               : 0x3a

The port_xmit_discard counter represents the total number of outbound
packets discarded by a port. Since the port numbers are above 2 I assume
these counters were obtained from an IB switch and not from an HCA ? The
InfiniBand specification defines when an IB switch is allowed to discard
packets.

Does the IB switch these counters come from support congestion control ?
IB switches that do not support congestion control discard packets
instead of sending FECNs (Forward Explicit Congestion Notifications).

Bart.