linux-kernel - Re: Irq architecture for multi-core network driver.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <m13a5apmm0.fsf@fess.ebiederm.org>
Date:	Fri, 23 Oct 2009 00:59:03 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	David Daney <ddaney@...iumnetworks.com>
Cc:	Chris Friesen <cfriesen@...tel.com>, netdev@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mips <linux-mips@...ux-mips.org>
Subject: Re: Irq architecture for multi-core network driver.

David Daney <ddaney@...iumnetworks.com> writes:

> Chris Friesen wrote:
>> On 10/22/2009 03:40 PM, David Daney wrote:
>>
>>> The main problem I have encountered is how to fit the interrupt
>>> management into the kernel framework.  Currently the interrupt source
>>> is connected to a single irq number.  I request_irq, and then manage
>>> the masking and unmasking on a per cpu basis by directly manipulating
>>> the interrupt controller's affinity/routing registers.  This goes
>>> behind the back of all the kernel's standard interrupt management
>>> routines.  I am looking for a better approach.
>>>
>>> One thing that comes to mind is that I could assign a different
>>> interrupt number per cpu to the interrupt signal.  So instead of
>>> having one irq I would have 32 of them.  The driver would then do
>>> request_irq for all 32 irqs, and could call enable_irq and disable_irq
>>> to enable and disable them.  The problem with this is that there isn't
>>> really a single packets-ready signal, but instead 16 of them.  So If I
>>> go this route I would have 16(lines) x 32(cpus) = 512 interrupt
>>> numbers just for the networking hardware, which seems a bit excessive.
>>
>> Does your hardware do flow-based queues?  In this model you have
>> multiple rx queues and the hardware hashes incoming packets to a single
>> queue based on the addresses, ports, etc. This ensures that all the
>> packets of a single connection always get processed in the order they
>> arrived at the net device.
>>
>
> Indeed, this is exactly what we have.
>
>
>> Typically in this model you have as many interrupts as queues
>> (presumably 16 in your case).  Each queue is assigned an interrupt and
>> that interrupt is affined to a single core.
>
> Certainly this is one mode of operation that should be supported, but I would
> also like to be able to go for raw throughput and have as many cores as possible
> reading from a single queue (like I currently have).

I believe will detect false packet drops and ask for unnecessary
retransmits if you have multiple cores processing a single queue,
because you are processing the packets out of order.

Eric
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/