On Fri, May 07, 2010 at 04:11:42PM +0200, Pavel Machek wrote: > Hi! > > > hotplug emulator: Abstract cpu register functions > > > > Abstract function arch_register_cpu and register_cpu, move the implementation > > details to a sub function with prefix "__". > > > > each of the sub function has an extra parameter nid, it can be used to register > > CPU under a fake NUMA node, it is a reserved interface for cpu hotplug emulation > > (CPU PROBE/RELEASE) in x86. > > I don't get it. CPU hotplug can already be tested using echo 0/1 > > online, and that works on 386. How is this different? > > It seems to add some numa magic. Why is it important? Pavel, it is not an easy thing to understand the full story since you may not work on this project so you have such question. Let me do a simpe introductions about the background. We need to understand 2 differnets concepts if you wnat to know the reason why we develop the hotplug emulaor. - CPU logcial online/offline it is the existed feature which you mentioned, we can online/offline CPUs throu sysfs interface /sys/device/system/cpu/cpuX/online (X is an integer, it stands for the CPU number) echo 0/1 > /sys/device/cpu/cpuX/online This is is logical CPU online/offline, when we do such operation, the CPU is already pluged into the motherboard, and the OS initialized the CPU. the data structure and CPU entries on sysfs are created, the CPU present mask and possible mask are setted, it does not refer to any physical hardware. the CPU status becomes online from offline, and ready to schedule to run process by scheduler. CPU online/offline is control by the kernel option CONFIG_HOTPLUG_CPU. - CPU hot-add/hot-remove This is physical CPU hot-add/hot-remove into motherboard, without shutdown the machine, after the hot-add operation, the new CPU will be powered on, and the OS recognize the new CPUs throu SCI interrupts, then OS intializes the new CPUs, create the related CPU structures, create sysfs entries for the new CPUs. Once all done, the CPU is ready to logcial online. The process to hot-add CPU: 1) Physical CPU hot-add to motherboard when after the machine is powered on 2) the BIOS send SCI interrupts to notice the OS 3) Linux hotplug handler parse the data from the acpi_handle data 4) hotplug handler initialize the CPU structure according the cpu ACPI data Current situation: 1) Provides developers an envronment Only very few hardware can support CPU hot-add/hot-remove, we need create an working environment for developers to write and debug hotplug code even through they do not has such hardward on hand. It is what NUMA hotplug emulator does exactly. Physcial hotplug emuator should be a better name. We have 2 solutions to solve this problem, and this one is selected finally; if you want to know more about the solutions, we can continue to on this thread. 2) Offers an automation test inferface for Linux CPU hot-add/hot-remove code Linux hot-add/hot-remove code has obvious bugs, but we do not see any automation test suite for it, even in LTP project(LTP has hotplug suite for logical CPU online/offline). It is a know diffcult work to test physcial hot-add/hot-remove code in automation way, but the hotplug emualtor does a good job for it. We reproduce all the major hotlug bugs against the internal emulator v2 and v3. We are sharing it to the community, wish more wisdoms and talents are included in it. We want to show an exmaple of software emualtion, and hopes more guys benifit from it, this is the purpose for this group patches. PowerPC supporting For ppc, it was added about half year ago by Nathan Fontenot, but x86 does not has such feature. Thanks for lethal to mention it, we already did some researching about it, I will reply it in another thread. commit 12633e803a2a556f6469e0933d08233d0844a2d9 Author: Nathan Fontenot <nfont@xxxxxxxxxxxxxx> Date: Wed Nov 25 17:23:25 2009 +0000 commit 1a8061c46c46c960f715c597b9d279ea2ba42bd9 Author: Nathan Fontenot <nfont@xxxxxxxxxxxxxx> Date: Tue Nov 24 21:13:32 2009 +0000 We inherit the name style from ppc, CPU hot-add/hot-remove is called CPU probe/release in kernel, it was control by kernel option CONFIG_ARCH_CPU_PROBE_RELEASE. -- Thanks & Regards, Shaohui _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
