linux-kernel - Re: [PATCH] irqchip, gicv3-its, numa: Workaround for Cavium ThunderX erratum 23144

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Date:	Mon, 24 Aug 2015 21:58:53 +0530
From:	Ganapatrao Kulkarni <gpkulkarni@...il.com>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	Robert Richter <robert.richter@...iumnetworks.com>,
	Will Deacon <Will.Deacon@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Tirumalesh Chalamarla <tirumalesh.chalamarla@...iumnetworks.com>,
	Robert Richter <rric@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ganapatrao Kulkarni <ganapatrao.kulkarni@...iumnetworks.com>
Subject: Re: [PATCH] irqchip, gicv3-its, numa: Workaround for Cavium ThunderX
 erratum 23144

Hi Marc,

thanks for the suggestions.

On Mon, Aug 24, 2015 at 7:17 PM, Marc Zyngier <marc.zyngier@....com> wrote:
> On 24/08/15 14:27, Ganapatrao Kulkarni wrote:
>> On Mon, Aug 24, 2015 at 6:15 PM, Marc Zyngier <marc.zyngier@....com> wrote:
>
>>>>>>  static void its_enable_cavium_thunderx(void *data)
>>>>>>  {
>>>>>> -     struct its_node *its = data;
>>>>>> +     struct its_node __maybe_unused *its = data;
>>>>>>
>>>>>> -     its->flags |= ITS_FLAGS_CAVIUM_THUNDERX;
>>>>>> +#ifdef CONFIG_CAVIUM_ERRATUM_22375
>>>>>> +     its->flags |= ITS_WORKAROUND_CAVIUM_22375;
>>>>>> +     pr_info("ITS: Enabling workaround for 22375, 24313\n");
>>>>>> +#endif
>>>>>> +
>>>>>> +#ifdef CONFIG_CAVIUM_ERRATUM_23144
>>>>>> +     if (num_possible_nodes() > 1) {
>>>>>> +             its->numa_node = its_get_node_thunderx(its);
>>>>>
>>>>> I'd rather see numa_node being always initialized to something useful.
>>>>> If you're adding numa support, why can't this be initialized via
>>>>> standard topology bindings?
>>>> IIUC, topology defines only cpu topology.
>>>
>>> Well, welcome to a much more complex system where both your CPUs and
>>> your IOs have some degree of affinity. This needs to be described
>>> properly, and not hacked on the side.
>> ok, will add description for the function.
>
> I sense that you misunderstood what I meant. What I'd like to see is
> some topology information coming from DT, showing the relationship
> between a device (your ITS) and a given node (your socket). This can
> then be used from two purposes:
sure will post next version with changes as per you comments.
>
> - find the optimal affinity for a MSI so that it doesn't default to a
> foreign node (a reasonable performance expectation),
this can be done by adding dt associativity property to its node.
 i can send in next version of patch.
> - work around implementation bugs where an LPI cannot be routed to a
> redistributor that is on a foreign node.


>
> I really don't feel like adding a hack just for the second point, and
> I'd rather get the big picture right so that your workaround is just a
> special case of the generic one.
>
> Thanks,
>
>         M.
> --
> Jazz is not dead. It just smells funny...

thanks
Ganapat
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