Andrew Patterson wrote:
This is v2 of the "call _OSC support during root bridge discovery"
patchset. At Bjorn Helgaas's suggestion, I have merged all the MSI
handling patches into one patch. Kenji Kaneshige also noted that I was
not checking aspm_disabled before setting ASPM _OSC capabilities. This
has been fixed.
Kenji also noted that the pci_msi_enable can be changed in various
quirks after root bridge discovery, resulting in the incorrect setting
of the MSI _OSC capability. I do not yet have a solution for this problem.
Unfortunately, I don't have good idea about it yet too. In addition,
I don't understand how to handle the case if a feature is supported
but disabled by OS, from the PCI firmware spec.
If we should not set _OSC capabilities when it is supported but
disabled by OS, maybe we need also consider what we should do for
OSC_EXT_PCI_CONFIG_SUPPORT and OSC_PCI_SEGMENT_GROUPS_SUPPORT
if mmconfig is disabled, as well as aspm_disabled and pci_msi_enable.
By the way, Taku Izumi plan to post some patches to reduce _OSC
evaluation for _OSC control soon. I'm appreciate it if you will try
it on your big server.
Thanks,
Kenji Kaneshige
I still need Matthew Wilcox to sign off on the first two patches.
I recently reported a problem where a machine with close to a 100 PCIe
root bridges was taking half an hour to just call _OSC. The root
cause is the AER code calling:
pcie_osc_support_set(OSC_EXT_PCI_CONFIG_SUPPORT);
for each bridge. The pcie_osc_support_set() function also iterates
over each bridge, so _OSC is called a quadratic number of times.
One solution to this problem would be to just move the call to
pcie_osc_support_set() to aer_service_init(), so _OSC support is only
called on each bridge once.
Matthew Wilcox came up with a better solution. He says "Why should a
driver be calling pcie_osc_support_set() anyway? This is something
the PCI core should be taking care of for it."
Matthew provided a patch for this solution that I massaged into the
following patch series.
It creates a new function (pci_acpi_osc_support()) which is called
from pci_root.c before we call any other methods on the device (as
recommended by the ACPI spec). Since we know what capabilities the
system supports, individual modules do not now need to inform the core
of their support for various capabilities.
Some work that still needs to be done (provided by Matthew):
o All the existing _OSC code should be moved from pci-acpi.c to
pci_root.c. I also think the acpi_osc_data should be made part of
the acpi_pci_root struct, eliminating a separate allocation.
o We could also use an interface that iterates over all existing
busses calling _OSC with new flags. Shouldn't be hard, once it's
integrated into pci_root.c.
o Further ahead, we don't actually check that the bits we asked for
(in 'control') were actually granted to us. The PCI firmware spec
is quite explicit about interdependencies amongst the bits.
o We also need to re-evaluate _OSC when coming out of S4.
This patch series duplicates currently functionality while removing
our quadratic problem. I believe that it can be applied now while the
above new functionality can be implemented some time in the future.
This patch series applies to the linux-next branch of pci-2.6 git
repository. I expect it will also work with linux-next.
Diff stats:
drivers/acpi/pci_root.c | 12 ++++++++++++
drivers/pci/msi.c | 31 +++++++++++-------------------
drivers/pci/pci-acpi.c | 37 +++++++++++++-----------------------
drivers/pci/pci.c | 2 --
drivers/pci/pci.h | 2 --
drivers/pci/pcie/aer/aerdrv_acpi.c | 1 -
drivers/pci/pcie/aspm.c | 27 +++++++++-----------------
include/linux/pci-acpi.h | 14 +++-----------
include/linux/pci.h | 14 ++++++++++++++
9 files changed, 62 insertions(+), 78 deletions(-)
Commits:
- Include missing acpi.h file in pci-acpi.h.
- Call _OSC support during root bridge discovery.
- PCIe ASPM _OSC support capabilities called when root bridge added.
- PCIe AER _OSC support capabilities called when root bridge added.
- PCI MSI _OSC support capabilities called when root bridge added.
- Remove obsolete _OSC capability support functions.
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