Re: [PATCH v8 1/4] PCI: Add new PCIe Fabric End Node flag, PCI_DEV_FLAGS_NO_RELAXED_ORDERING

From: Casey Leedom
Date: Fri Aug 04 2017 - 17:06:25 EST

| From: Ding Tianhong <dingtianhong@xxxxxxxxxx>
| Sent: Thursday, August 3, 2017 6:44 AM
| diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
| index 6967c6b..1e1cdbe 100644
| --- a/drivers/pci/quirks.c
| +++ b/drivers/pci/quirks.c
| @@ -4016,6 +4016,44 @@ static void quirk_tw686x_class(struct pci_dev *pdev)
| quirk_tw686x_class);
| /*
| + * Some devices have problems with Transaction Layer Packets with the Relaxed
| + * Ordering Attribute set. Such devices should mark themselves and other
| + * Device Drivers should check before sending TLPs with RO set.
| + */
| +static void quirk_relaxedordering_disable(struct pci_dev *dev)
| +{
| + dev->dev_flags |= PCI_DEV_FLAGS_NO_RELAXED_ORDERING;
| +}
| +
| +/*
| + * Intel E5-26xx Root Complex has a Flow Control Credit issue which can
| + * cause performance problems with Upstream Transaction Layer Packets with
| + * Relaxed Ordering set.
| + */
| + quirk_relaxedordering_disable);
| + quirk_relaxedordering_disable);
| + quirk_relaxedordering_disable);
| + ...

It looks like this is missing the set of Root Complex IDs that were noted in
the document to which Patrick Cramer sent us a reference:

In section 3.9.1 we have:

3.9.1 Optimizing PCIe Performance for Accesses Toward Coherent Memory
and Toward MMIO Regions (P2P)

In order to maximize performance for PCIe devices in the processors
listed in Table 3-6 below, the soft- ware should determine whether the
accesses are toward coherent memory (system memory) or toward MMIO
regions (P2P access to other devices). If the access is toward MMIO
region, then software can command HW to set the RO bit in the TLP
header, as this would allow hardware to achieve maximum throughput for
these types of accesses. For accesses toward coherent memory, software
can command HW to clear the RO bit in the TLP header (no RO), as this
would allow hardware to achieve maximum throughput for these types of

Table 3-6. Intel Processor CPU RP Device IDs for Processors Optimizing
PCIe Performance

Processor CPU RP Device IDs

Intel Xeon processors based on 6F01H-6F0EH
Broadwell microarchitecture

Intel Xeon processors based on 2F01H-2F0EH
Haswell microarchitecture

The PCI Device IDs you have there are the first ones that I guessed at
having the performance problem with Relaxed Ordering. We now apparently
have a complete list from Intel.

I don't want to phrase this as a "NAK" because you've gone around the
mulberry bush a bunch of times already. So maybe just go with what you've
got in version 8 of your patch and then do a follow on patch to complete the