There have been some of failing cases of kdump in 2nd kernel, where ususally only one cpu is enabled by "nr_cpus=1", but with a large number of devices, which may easily exceed the maximum IRQ resources of one cpu can handle. As a result, the 2nd kernel will hang and kdump fails. This issue is often observed on machines with many cpus and many devices.
On those systems, pcieports consume quite proportion of IRQ resources, many following message can be seen in dmesg log:
pcieport 0000:18:01.0: PME: Signaling with IRQ 109
According to kernel doc1, when "pcie_ports=compat" applied, it will disable native PCIe services (PME, AER, DPC, PCIe hotplug). Those functions are power management events, error reporting, performance, hotplug related, which are not the must-have functions for kdump. In addition, after testing, no side effects such as cannot writing vmcore into sdx, nvme etc been noticed.
This patch will disable native PCIe services for 2nd kernel, to saving the scarce IRQ resources and increase the kdump success.
Attach Prarit's comments:
This makes sense to me. The only concern anyone should have is that a PCIE error could have been responsible for taking down the kernel in the first place, and booting into the second kernel could then also have a fatal problem. I'm not sure we can ever fix that type of cascade of panics :) so it makes sense to disable these features.
There have been some of failing cases of kdump in 2nd kernel, where ususally only one cpu is enabled by "nr_cpus=1", but with a large number of devices, which may easily exceed the maximum IRQ resources of one cpu can handle. As a result, the 2nd kernel will hang and kdump fails. This issue is often observed on machines with many cpus and many devices.
On those systems, pcieports consume quite proportion of IRQ resources, many following message can be seen in dmesg log:
pcieport 0000:18:01.0: PME: Signaling with IRQ 109
According to kernel doc1, when "pcie_ports=compat" applied, it will disable native PCIe services (PME, AER, DPC, PCIe hotplug). Those functions are power management events, error reporting, performance, hotplug related, which are not the must-have functions for kdump. In addition, after testing, no side effects such as cannot writing vmcore into sdx, nvme etc been noticed.
This patch will disable native PCIe services for 2nd kernel, to saving the scarce IRQ resources and increase the kdump success.
Attach Prarit's comments:
This makes sense to me. The only concern anyone should have is that a PCIE error could have been responsible for taking down the kernel in the first place, and booting into the second kernel could then also have a fatal problem. I'm not sure we can ever fix that type of cascade of panics :) so it makes sense to disable these features.
Acked-by: Prarit Bhargava prarit@redhat.com Acked-by: Dave Young dyoung@redhat.com