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

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Message-ID: <ZMmZO9IPmXNEB49t@ziepe.ca>
Date: Tue, 1 Aug 2023 20:46:03 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Long Li <longli@...rosoft.com>
Cc: Wei Hu <weh@...rosoft.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	Ajay Sharma <sharmaajay@...rosoft.com>,
	"leon@...nel.org" <leon@...nel.org>,
	KY Srinivasan <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	"wei.liu@...nel.org" <wei.liu@...nel.org>,
	Dexuan Cui <decui@...rosoft.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>,
	"pabeni@...hat.com" <pabeni@...hat.com>,
	vkuznets <vkuznets@...hat.com>,
	"ssengar@...ux.microsoft.com" <ssengar@...ux.microsoft.com>,
	"shradhagupta@...ux.microsoft.com" <shradhagupta@...ux.microsoft.com>
Subject: Re: [PATCH v4 1/1] RDMA/mana_ib: Add EQ interrupt support to mana ib
 driver.

On Tue, Aug 01, 2023 at 07:06:57PM +0000, Long Li wrote:

> The driver interrupt code limits the CPU processing time of each EQ
> by reading a small batch of EQEs in this interrupt. It guarantees
> all the EQs are checked on this CPU, and limits the interrupt
> processing time for any given EQ. In this way, a bad EQ (which is
> stormed by a bad user doing unreasonable re-arming on the CQ) can't
> storm other EQs on this CPU.

Of course it can, the bad use just creates a million EQs and pushes a
bit of work through them constantly. How is that really any different
from pushing more EQEs into a single EQ?

And how does your EQ multiplexing work anyhow? Do you poll every EQ on
every interrupt? That itself is a DOS vector.

Jason