Re: [PATCH] arm64: enable ARCH_WANT_RELAX_ORDER for aarch64

[Ding Tianhong <dingtianhong@huawei.com>]

On 2017/3/20 22:00, Robin Murphy wrote:
> On 14/03/17 14:06, Ding Tianhong wrote:
>> Hi Robin：
>>
>> On 2017/3/13 21:31, Robin Murphy wrote:
>>> On 13/03/17 12:03, Ding Tianhong wrote:
>>>> The ARCH_WANT_RELAX_ORDER will enable Relaxed Ordering (RO) which allows
>>>> transactions that do not have any order of completion requirements to
>>>> complete more efficiently compare to the Stricted Ordering (SO) for ixbge
>>>> nic card.
>>>
>>> Which ixgbe NIC? As far as I can see we have an arch-level config option
>>> here which applies to one single driver, and doesn't even cover all the
>>> hardware supported by that driver (82598, for example, still has the
>>> #ifndef CONFIG_SPARC in the equivalent place). Looking at the history,
>>> I'd prefer to at least know what the "various issues with certain
>>> chipsets" were, and why they wouldn't affect ARM systems,  before making
>>> any judgement about whether this could be considered universally safe
>>> for arm64.
>>>
>>
>> Indeed, in fact if the chipsets didn't support RO mode or has some errata for RO mode, it may
>> occur some issues, but it looks no such aarch64 chips, maybe I miss something.
>>
>> There are several intel nic card could support enable relax order, so need another patch to rename the SPARC
>> to ARCH_WANT_RELAX_ORDER, the universal name looks more better.
> 
> I'm sure I'm not alone in disagreeing outright that it looks better,
> because ARCH_ is hardly the appropriate namespace for a driver option
> unrelated to an architecture port's interaction with core kernel code;
> plus it's further confounded by a name which both doesn't imply any
> relationship with said driver, and does overlap with the kind of CPU
> memory model terminology which *is* the purview of architecture ports.
> 
> As an equivalent example, consider how equally misleading it would be
> from the ARM maintainer perspective if CONFIG_IOMMU_IO_PGTABLE_LPAE was
> just called CONFIG_ARCH_WANT_LPAE and implemented in this manner.
> 
> Having looked into it, I see that "Relaxed Order" does actually turn out
> to be a specific PCIe term, but even in that context it doesn't apply at
> the arch level - that's going to be a matter for particular endpoints
> and particular host controllers and all the quirks in between.
> 
>>>> The system will see high write-to-memory performance when RO is
>>>> enabled on the data transactions just like the SPARC did.
>>>>
>>>> The aarch64 pcie controller could both support Relaxed Ordering (RO)
>>>
>>> What is "the AArch64 PCIe controller", exactly? Disregarding that
>>> talking of PCIe in terms of the CPU ISA makes little sense, I can barely
>>> name two ARMv8-based systems which nominally use the same PCIe IP, and
>>> the amount of various quirks and incompatibilities I'm aware of leaves
>>> me with the default assumption that any such unqualified blanket
>>> statement is probably wrong. I think we need some much more considered
>>> reasoning here.
>>>
>>
>> Agree, till now I could only test on hip06/hip07 board and get the better performance,
>> maybe I could test on other aarch64 platform.
>>
>>>> and Stricted Ordering (SO), so enable ARCH_WANT_RELAX_ORDER for ixgbe
>>>> nic card to get much more better performance, and didn't see any
>>>> adverse effects.
>>>>
>>>> Nic Card(Ixgbe)			Disable RO	|	Enable RO
>>>> Performance(Per thread)		8.4Gb/s		|	9.4Gb/s
>>>>
>>>> Tested by Iperf on Hip06/Hip07 Soc Board.
>>>>
>>>> Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
>>>> ---
>>>>  arch/arm64/Kconfig | 1 +
>>>>  1 file changed, 1 insertion(+)
>>>>
>>>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>>>> index 8c7c244..36249a3 100644
>>>> --- a/arch/arm64/Kconfig
>>>> +++ b/arch/arm64/Kconfig
>>>> @@ -115,6 +115,7 @@ config ARM64
>>>>  	select SPARSE_IRQ
>>>>  	select SYSCTL_EXCEPTION_TRACE
>>>>  	select THREAD_INFO_IN_TASK
>>>> +	select ARCH_WANT_RELAX_ORDER
>>>
>>> I'd say the first order of business is to rename this config option to
>>> IXBGE_82599_WANT_RELAXED_ORDER so that it's not entirely misleading and
>>
>> not only for 82599, including 82598, 82576....
> 
> So why does ixgbe_start_hw_82598() still have the original #ifndef
> CONFIG_SPARC from 887012e80aea?
> 
> It was pretty clear from the outset that this is one of those patches
> for making a particular card go faster in a particular system based on
> what's available in the test lab - there's nothing inherently wrong with
> that, but if it were presented merely in those terms there would
> probably be a lot less to object to.
> 
>>> ambiguous. At first glance it looks far more like something scary to do
>>> with memory barriers than a network driver option. Howcome this isn't
>>> just in drivers/net/intel/Kconfig as a "default y if SPARC" bool anyway?
>>
>> didn't see any essential differences, and I still need to get some Acked by arm maintainer.
> 
> The big difference is that had people done the sensible thing by adding,
> say, CONFIG_IXGBE_ALLOW_RELAXED_ORDER to drivers/net/intel/... and
> sending a self-contained patch through the net tree, architecture
> maintainers wouldn't even need to be aware, let alone ack anything. Then
> in future if someone sends another patch against the net tree changing
> "y if (SPARC || ARM64)" back to "y if SPARC" because it happens to break
> on their system, the resulting discussion and resolution can happen on
> netdev, and architecture maintainers who aren't necessarily familiar
> with particular ixgbe/PCIe hardware details *still* don't need to care.
> 
> Robin.
> 

Ok, after a period of thinking and verification, I believe it is not only affect for hisilicon,
and will try to find a better way to fix this according to your opinions, thanks.

Ding

> .
>