在 2020/6/30 3:57, Raj, Ashok 写道:
> Hi Bjorn
> On Mon, Jun 29, 2020 at 02:33:16PM -0500, Bjorn Helgaas wrote:
>> [+cc Ashok, Ding, Casey]
>> On Mon, Jun 29, 2020 at 12:32:44PM +0300, Aya Levin wrote:
>>> I wanted to turn on RO on the ETH driver based on
>>> pcie_relaxed_ordering_enabled().
>>> From my experiments I see that pcie_relaxed_ordering_enabled() return true
>>> on Intel(R) Xeon(R) CPU E5-2650 v3 @ 2.30GHz. This CPU is from Haswell
>>> series which is known to have bug in RO implementation. In this case, I
>>> expected pcie_relaxed_ordering_enabled() to return false, shouldn't it?
>> Is there an erratum for this?  How do we know this device has a bug
>> in relaxed ordering?
> https://software.intel.com/content/www/us/en/develop/download/intel-64-and-ia-32-architectures-optimization-reference-manual.html
> For some reason they weren't documented in the errata, but under
> Optimization manual :-)
> Table 3-7. Intel Processor CPU RP Device IDs for Processors Optimizing PCIe
> Performance
> Processor CPU RP Device IDs
> Intel Xeon processors based on Broadwell microarchitecture 6F01H-6F0EH
> Intel Xeon processors based on Haswell microarchitecture 2F01H-2F0EH
> These are the two that were listed in the manual. drivers/pci/quirks.c also
> has an eloborate list of root ports where relaxed_ordering is disabled. Did
> you check if its not already covered here?
> Send lspci if its not already covered by this table.

Looks like the chip series is not in the errta list, but it is really difficult 
to distinguish and test.

>>> In addition, we are worried about future bugs in new CPUs which may result
>>> in performance degradation while using RO, as long as the function
>>> pcie_relaxed_ordering_enabled() will return true for these CPUs. 
>> I'm worried about this too.  I do not want to add a Device ID to the
>> quirk_relaxedordering_disable() list for every new Intel CPU.  That's
>> a huge hassle and creates a real problem for old kernels running on
>> those new CPUs, because things might work "most of the time" but not
>> always.
> I'll check when this is fixed, i was told newer ones should work properly.
> But I'll confirm.

Maybe prevent the Relax Ordering for all Intel CPUs is a better soluton, looks 
it will not break anything.

> .

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