On Mon, 2013-11-04 at 11:51 +0100, Vasilis Liaskovitis wrote: > Any comment on this? > > On Fri, Oct 25, 2013 at 11:32:10AM +0200, Vasilis Liaskovitis wrote: > > This patch adds a _PXM object to seabios CPU objects. The _PXM value is derived > > from CPU SRAT entries, so build_ssdt needs to be called after build_srat for > > this to work. > > > > The motivation for this patch is a CPU hot-unplug/hot-plug bug observed when > > using seabios and a 3.11 linux guest kernel on a multi-NUMA node qemu/kvm VM. > > The linux guest kernel parses the SRAT CPU entries at boot time and stores them > > in the array __apicid_to_node. When a CPU is hot-removed, the linux guest kernel > > resets the removed CPU's __apicid_to_node entry to NO_NUMA_NODE (kernel commit > > c4c60524). When the removed cpu is hot-added again, the linux kernel looks up > > the hot-added cpu object's _PXM value instead of somehow re-using the SRAT > > entry info (acpi_map_cpu2node calls acpi_get_node which calls acpi_get_pxm). If > > the _PXM value is not found, the CPU is assumed to be on node 0, and it is > > hot-plugged in the wrong NUMA node. > > > > Which is the preferred OSPM way of looking up a CPU's proximity info at hotplug > > time? Is it the CPU object's _PXM value, or the already-parsed CPU SRAT entry? > > Or maybe both ways are valid? SRAT describes proximity values at boot-time. During hotplug, the kernel is supposed to obtain the current proximity value from _PXM method. > > This issue may require a kernel fix alternatively or additionally to the seabios > > fix: The kernel can save the originally parsed SRAT entry info somewhere before > > it resets it at hot-remove time, and use that info on hot-plug time if the _PXM > > value is missing for the hot-plugged CPU BIOS object. This way CPU hot-plug > > works well against a BIOS with no CPU _PXM info. To support CPU hotplug, seabios needs to implement _PXM to CPU or its parent device object when the system has multiple nodes. Thanks, -Toshi -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
