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SubjectRe: [PATCH] irqchip/gic-v3-its: Add workaround for ThunderX2 erratum #174
On Wed, Jan 3, 2018 at 5:06 PM, Marc Zyngier <marc.zyngier@arm.com> wrote:
> On 03/01/18 11:20, Ganapatrao Kulkarni wrote:
>> On Wed, Jan 3, 2018 at 3:43 PM, Marc Zyngier <marc.zyngier@arm.com> wrote:
>>> On 03/01/18 09:35, Ganapatrao Kulkarni wrote:
>>>> Hi Marc,
>>>>
>>>> On Wed, Jan 3, 2018 at 2:17 PM, Marc Zyngier <marc.zyngier@arm.com> wrote:
>>>>> On 03/01/18 06:32, Ganapatrao Kulkarni wrote:
>>>>>> When an interrupt is moved across node collections on ThunderX2
>>>>>
>>>>> node collections?
>>>>
>>>> ok, i will rephrase it.
>>>> i was intended to say cross NUMA node collection/cpu affinity change.
>>>>
>>>>>
>>>>>> multi Socket platform, an interrupt stops routed to new collection
>>>>>> and results in loss of interrupts.
>>>>>>
>>>>>> Adding workaround to issue INV after MOVI for cross-node collection
>>>>>> move to flush out the cached entry.
>>>>>>
>>>>>> Signed-off-by: Ganapatrao Kulkarni <ganapatrao.kulkarni@cavium.com>
>>>>>> ---
>>>>>> Documentation/arm64/silicon-errata.txt | 1 +
>>>>>> arch/arm64/Kconfig | 11 +++++++++++
>>>>>> drivers/irqchip/irq-gic-v3-its.c | 24 ++++++++++++++++++++++++
>>>>>> 3 files changed, 36 insertions(+)
>>>>>>
>>>>>> diff --git a/Documentation/arm64/silicon-errata.txt b/Documentation/arm64/silicon-errata.txt
>>>>>> index fc1c884..fb27cb5 100644
>>>>>> --- a/Documentation/arm64/silicon-errata.txt
>>>>>> +++ b/Documentation/arm64/silicon-errata.txt
>>>>>> @@ -63,6 +63,7 @@ stable kernels.
>>>>>> | Cavium | ThunderX Core | #27456 | CAVIUM_ERRATUM_27456 |
>>>>>> | Cavium | ThunderX Core | #30115 | CAVIUM_ERRATUM_30115 |
>>>>>> | Cavium | ThunderX SMMUv2 | #27704 | N/A |
>>>>>> +| Cavium | ThunderX2 ITS | #174 | CAVIUM_ERRATUM_174 |
>>>>>> | Cavium | ThunderX2 SMMUv3| #74 | N/A |
>>>>>> | Cavium | ThunderX2 SMMUv3| #126 | N/A |
>>>>>> | | | | |
>>>>>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>>>>>> index c9a7e9e..71a7e30 100644
>>>>>> --- a/arch/arm64/Kconfig
>>>>>> +++ b/arch/arm64/Kconfig
>>>>>> @@ -461,6 +461,17 @@ config ARM64_ERRATUM_843419
>>>>>>
>>>>>> If unsure, say Y.
>>>>>>
>>>>>> +config CAVIUM_ERRATUM_174
>>>>>> + bool "Cavium ThunderX2 erratum 174"
>>>>>> + depends on NUMA
>>>>>
>>>>> Why? This system will be affected no matter whether NUMA is selected or not.
>>>>
>>>> it does not makes sense to enable on non-NUMA/single socket platforms.
>>>> By default NUMA is enabled on ThunderX2 dual socket platforms.
>>>
>>> <quote>
>>> config ARCH_THUNDER2
>>> bool "Cavium ThunderX2 Server Processors"
>>> select GPIOLIB
>>> help
>>> This enables support for Cavium's ThunderX2 CN99XX family of
>>> server processors.
>>> </quote>
>>>
>>> Do you see any NUMA here? I can perfectly compile a kernel with both
>>> sockets, and not using NUMA. NUMA has to do with memory, and not interrupts.
>>
>> ok, i will remote it.
>>>
>>>>
>>>>>
>>>>>> + default y
>>>>>> + help
>>>>>> + LPI stops routed to redistributors after inter node collection
>>>>>> + move in ITS. Enable workaround to invalidate ITS entry after
>>>>>> + inter-node collection move.
>>>>>
>>>>> That's a very terse description. Nobody knows what an LPI, a
>>>>> redistributor or a collection is. Please explain what the erratum is in
>>>>> layman's terms (Cavium ThunderX2 systems may loose interrupts on
>>>>> affinity change) so that people understand whether or not they are affected.
>>>>
>>>> ok, i will rephrase it in next version.
>>>>>
>>>>>> +
>>>>>> + If unsure, say Y.
>>>>>> +
>>>>>> config CAVIUM_ERRATUM_22375
>>>>>> bool "Cavium erratum 22375, 24313"
>>>>>> default y
>>>>>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>>>>>> index 06f025f..d8b9c96 100644
>>>>>> --- a/drivers/irqchip/irq-gic-v3-its.c
>>>>>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>>>>>> @@ -46,6 +46,7 @@
>>>>>> #define ITS_FLAGS_CMDQ_NEEDS_FLUSHING (1ULL << 0)
>>>>>> #define ITS_FLAGS_WORKAROUND_CAVIUM_22375 (1ULL << 1)
>>>>>> #define ITS_FLAGS_WORKAROUND_CAVIUM_23144 (1ULL << 2)
>>>>>> +#define ITS_FLAGS_WORKAROUND_CAVIUM_174 (1ULL << 3)
>>>>>>
>>>>>> #define RDIST_FLAGS_PROPBASE_NEEDS_FLUSHING (1 << 0)
>>>>>>
>>>>>> @@ -1119,6 +1120,12 @@ static int its_set_affinity(struct irq_data *d, const struct cpumask *mask_val,
>>>>>> if (cpu != its_dev->event_map.col_map[id]) {
>>>>>> target_col = &its_dev->its->collections[cpu];
>>>>>> its_send_movi(its_dev, target_col, id);
>>>>>> + if (its_dev->its->flags & ITS_FLAGS_WORKAROUND_CAVIUM_174) {
>>>>>> + /* Issue INV for cross node collection move. */
>>>>>> + if (cpu_to_node(cpu) !=
>>>>>> + cpu_to_node(its_dev->event_map.col_map[id]))
>>>>>> + its_send_inv(its_dev, id);
>>>>>> + }
>>>>>
>>>>> What happens if an interrupt happens after the MOV, but before the INV?
>>>>
>>>> there can be drop, if interrupt happens before INV, however, it is
>>>> highly unlikely that we will hit the issue since MOVI and INV are
>>>> executed back to back. this workaround fixed issue seen on couple of
>>>> IOs.
>>>
>>> Really? So this doesn't fix anything, and the device may just wait
>>> forever for the CPU to service an LPI that was never delivered. I'm
>>> sorry, but that's not an acceptable workaround.
>>>
>>> I can see two solutions:
>>> 1) you inject an interrupt after the INV as you may have lost at least one
>>> 2) you restrict the affinity of LPIs to a single socket
>>>
>>> (1) will generate spurious interrupts, but will be safe. (2) will result
>>> in an unbalanced system. Pick your poison...
>>>
>>> You may be able to achieve something by disabling the LPI before
>>> performing the MOVI/INV sequence, and reenable it afterwards, but only
>>> you can tell if this could work with your HW.
>>
>> thanks for the suggestion, i will try out disable/enable LPI.
>> the sequence would be,
>> Disable LPI in rdist of cpu1
>> MOVI from cpu1 to cpu2
>> INV
>> enable LPI in rdist of cpu1
>
> You cannot disable LPIs at the redistributor level. For a start, this is
> not allowed by the architecture. It would also result in all the other
> LPIs to be lost. What you can do is to disable the single LPI you're
> about to move:
>
> its_mask_irq(d);
> MOVI
> its_unmask_irq(d);

thanks, this also fixes the issue.
i shall post v2 with this sequence.

>
> This will result in an INV/MOVI/INV sequence. Hopefully your MOVI
> implementation can move pending bits. But I don't know if that's enough,
> given the description of the erratum. And the more I think of it, the
> less I think it is a viable workaround.

>
> I'm starting to believe that something similar to
> ITS_FLAGS_WORKAROUND_CAVIUM_23144 is the way to go.
>
> Thanks,
>
> M.
> --
> Jazz is not dead. It just smells funny...

thanks
Ganapat

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