Re: [PATCH v4 1/1] RDMA/mana_ib: Add EQ interrupt support to mana ib driver.

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On Fri, Jul 28, 2023 at 05:51:46PM +0000, Long Li wrote:
> > Subject: Re: [PATCH v4 1/1] RDMA/mana_ib: Add EQ interrupt support to mana ib
> > driver.
> > 
> > On Fri, Jul 28, 2023 at 05:07:49PM +0000, Wei Hu wrote:
> > > Add EQ interrupt support for mana ib driver. Allocate EQs per ucontext
> > > to receive interrupt. Attach EQ when CQ is created. Call CQ interrupt
> > > handler when completion interrupt happens. EQs are destroyed when
> > > ucontext is deallocated.
> > 
> > It seems strange that interrupts would be somehow linked to a ucontext?
> > interrupts are highly limited, you can DOS the entire system if someone abuses
> > this.
> > 
> > Generally I expect a properly functioning driver to use one interrupt per CPU core.
> 
> Yes, MANA uses one interrupt per CPU. One interrupt is shared among multiple
> EQs.

So you have another multiplexing layer between the interrupt and the
EQ? That is alot of multiplexing layers..

> > You should tie the CQ to a shared EQ belong to the core that the CQ wants to have
> > affinity to.
> 
> The reason for using a separate EQ for a ucontext, is for preventing DOS. If we use
> a shared EQ, a single ucontext can storm this shared EQ affecting
> other users.

With a proper design it should not be possible. The CQ adds an entry
to the EQ and that should be rate limited by the ability of userspace
to schedule to re-arm the CQ.

Jason



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