[ofa-general] [PATCH] ipoib/cm: use common CQ for all TX QPs

[Michael S. Tsirkin]

> Quoting Pradeep Satyanarayana <pradeeps at linux.vnet.ibm.com>:
> Subject: Re: [ofa-general] [PATCH] ipoib/cm: use common CQ for all TX QPs
> 
> Michael S. Tsirkin wrote:
> > Use common CQ for all TX QPs: keep a per-device counter of outstanding TX WRs,
> > and stop the interface when this counter reaches the send queue size, to avoid
> > CQ overruns.  This should help reduce the number of interrupts for
> > bi-directional traffic (such as TCP).
> 
> CQ overrun generates asynchronous errors. If CQ overruns are avoided, how does that 
> reduce interrupts?
> 
> On a side note, as a further extension to this idea, would it be worth considering 
> sendq_size and recvq_size being device specific in the future, instead of being 
> module specific?

How would you do this without resize QP support in low leve drivers?

> > This helps fix "driver is hogging interrupts" errors reported for IPoIB send side.
> > See e.g. https://bugs.openfabrics.org/show_bug.cgi?id=508
> > 
> In bug 508, timer ticks were lost because some device was hogging interrupts. 
> What is the association between dropping packets and hogging interrupts?
> Can you expand on that?

This patch fixes the hogging interrupts problem by polling TX completions
from NAPI thread.

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MST