Hi Bjorn, thanks for the response. > > On systems that have PCIe ASPM support in the BIOS enabled the commit > > 387d37577fdd05e9472c20885464c2a53b3c945f may lead to the situation > > that accesses to registers of enabled PCIe devices are extremely slow. > > This happens if the ACPI FADT declares incorrectly that the system > > doesn't support PCIe ASPM even if this is enabled in the BIOS. > > In this case the function pcie_no_aspm() will be called. > > However this sets the aspm_policy to POLICY_DEFAULT even if > > CONFIG_PCIEASPM_PERFORMANCE has been configured. > > As result, the ASPM on a PCIe may still be set even if this is not > > expected. > > > > This happens e.g. on a HP workstation 800 G1 together with an Intel > > dual port Ethernet server adapter i350 plugged in. > > Whenever ASPM is enabled in the BIOS the access to the LAN registers > > are really slow (read access: slower than 20us). > > In this setup the LnkCap of the two LAN controllers and of the > > integrated PCIe switch is set to "ASPM L1 Enabled" > > even if the controller is configured to be up and running. > > There has been a lengthy discussion on this performance issue due to > > this issue on the linux-rt-users list: > > http://marc.info/?l=linux-rt-users&m=147454824515022&w=2 > > > > This patch solves this issue by forcing to disable ASPM if > > CONFIG_PCIEASPM_PERFORMANCE has been set. > > The 387d37577fdd changelog says that when ACPI_FADT_NO_ASPM is set, the > expected behavior is for the OS to not touch the ASPM configuration, and that this is > what Windows does. > > If I understand correctly, your proposal in this patch is to change this so that if > ACPI_FADT_NO_ASPM is set and CONFIG_PCIEASPM_PERFORMANCE=y, > we go ahead and disable ASPM. > > Only the firmware author can tell whether it's really a bug that this system sets > ACPI_FADT_NO_ASPM. It could be that there's some platform issue that is > avoided by leaving the BIOS ASPM configuration untouched. > > If it really *is* a firmware bug, and ACPI_FADT_NO_ASPM is not supposed to be > set on this platform, CONFIG_PCIEASPM_PERFORMANCE doesn't feel like the > right mechanism for working around it. It should be safe to enable that for all > systems, and for other systems that set ACPI_FADT_NO_ASPM correctly, we > should not touch ASPM configuration. > > Can you open a bugzilla at http://bugzilla.kernel.org and attach the complete dmesg > log and "lspci -vv" output? This is a subtle area where we've had many break/fix > cycles, and it's important to be able to go back and look at details of problems that > motivated previous changes. > I have create a new bug report (id=189951). https://bugzilla.kernel.org/show_bug.cgi?id=189951 Regards Mathias -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
