Linux Works Towards True CPU Hotplug Support

[bridgman]

Yes, one basically replaces the CPU with bare hands, though you have to do it quickly, typically between 2 CPU cycles to not lose data. The motherboard detects that the CPU is being swapped and sends the OS a notification signal to work without the CPU, in which case the OS switches to using the audio or GPU processor (which makes it work slightly more slowly) until the new CPU is put in and the system continues working as usual.

2 cycles? a 4mhz processor has 4million cycles per second (http://www.codepedia.com/1/CPU+cycles) therefore a my 1.6ghz dualcore i5 is at 3.2billion (1.6billion per core) PER SECOND? Soo...its impossible to swap them out within 2 cycles?

I think cl333r might be having a bit of fun

Normally the backplane in a hot swap system would have per-module power controllers and/or data buffers so that a module can be unplugged and replaced without affecting any of the other modules. Typical systems would have a number of modules of each type (CPU, disk, maybe even power supply) so that when one module was removed processing could continue on the remaining modules.

Any work on the failed/removed CPU/memory module would be lost, so any affected process would need to be restarted or restored from a checkpoint. For a disk module, the RAID software/firmware would handle it.

[Ericg]

Yes, one basically replaces the CPU with bare hands, though you have to do it quickly, typically between 2 CPU cycles to not lose data. The motherboard detects that the CPU is being swapped and sends the OS a notification signal to work without the CPU, in which case the OS switches to using the audio or GPU processor (which makes it work slightly more slowly) until the new CPU is put in and the system continues working as usual.

2 cycles? a 4mhz processor has 4million cycles per second (http://www.codepedia.com/1/CPU+cycles) therefore a my 1.6ghz dualcore i5 is at 3.2billion (1.6billion per core) PER SECOND? Soo...its impossible to swap them out within 2 cycles?

[[Knuckles]]

Yes, one basically replaces the CPU with bare hands, though you have to do it quickly, typically between 2 CPU cycles to not lose data. The motherboard detects that the CPU is being swapped and sends the OS a notification signal to work without the CPU, in which case the OS switches to using the audio or GPU processor (which makes it work slightly more slowly) until the new CPU is put in and the system continues working as usual.

In cases where the GPU is in the same silicon as the cpu, you could also temporarily switch to an ARM cpu inside an SSD controller. After all, many of them nowadays are multicores too!

[cl333r]

Yes, one basically replaces the CPU with bare hands, though you have to do it quickly, typically between 2 CPU cycles to not lose data. The motherboard detects that the CPU is being swapped and sends the OS a notification signal to work without the CPU, in which case the OS switches to using the audio or GPU processor (which makes it work slightly more slowly) until the new CPU is put in and the system continues working as usual.

[Ericg]

Phoronix: Linux Works Towards True CPU Hotplug Support

One of the first pull requests sent in following the the Linux 3.7 kernel release is for getting closer to "true CPU hotplug support" with the Linux 3.8 kernel...

http://www.phoronix.com/vr.php?view=MTI0ODc

Disclaimer: I havent been hands-on with server hardware, im looking at this with the perspective of a desktop system.

Whats the usefulness of this? When I think of hotplugging I think of swapping out the piece of hardware while its in use which is why I get confused when I read about hot-swappable drives/ram/CPU's. If you just pull out a stick of RAM or a CPU while its in us you'll lose whatever data was on it and isnt it a risk to whoever is pulling out said piece of hardware from the electrical charge of the system? I get that hardware goes bad and it needs to be replaced but I guess where im tripping up on is the actual procedure to follow FOR replacing it while the systems in use.

[phoronix]

Phoronix: Linux Works Towards True CPU Hotplug Support

One of the first pull requests sent in following the the Linux 3.7 kernel release is for getting closer to "true CPU hotplug support" with the Linux 3.8 kernel...

http://www.phoronix.com/vr.php?view=MTI0ODc