Hi,
This patch implements SMP alternatives, i.e. switching at runtime
between different code versions for UP and SMP. The code can patch both
SMP->UP and UP->SMP. The UP->SMP case is useful for CPU hotplug.
With CONFIG_CPU_HOTPLUG enabled the code switches to UP at boot
time and when the number of CPUs goes down to 1, and switches to
SMP when the number of CPUs goes up to 2.
Without CONFIG_CPU_HOTPLUG or on non-SMP-capable systems the code
is patched once at boot time (if needed) and the tables are
released afterwards.
The changes in detail:
* The current alternatives bits are moved to a separate file,
the SMP alternatives code is added there.
* The patch adds some new elf sections to the kernel:
.smp_altinstructions
like .altinstructions, also contains a list
of alt_instr structs.
.smp_altinstr_replacement
like .altinstr_replacement, but also has some space to
save original instruction before replaving it.
.smp_locks
list of pointers to lock prefixes which can be nop'ed
out on UP.
The first two are used to replace more complex instruction
sequences such as spinlocks and semaphores. It would be possible
to deal with the lock prefixes with that as well, but by handling
them as special case the table sizes become much smaller.
* The sections are page-aligned and padded up to page size, so they
can be free if they are not needed.
* Splitted the code to release init pages to a separate function and
use it to release the elf sections if they are unused.
please apply,
Gerd
This patch implements SMP alternatives, i.e. switching at runtime
between different code versions for UP and SMP. The code can patch both
SMP->UP and UP->SMP. The UP->SMP case is useful for CPU hotplug.
With CONFIG_CPU_HOTPLUG enabled the code switches to UP at boot
time and when the number of CPUs goes down to 1, and switches to
SMP when the number of CPUs goes up to 2.
Without CONFIG_CPU_HOTPLUG or on non-SMP-capable systems the code
is patched once at boot time (if needed) and the tables are
released afterwards.
The changes in detail:
* The current alternatives bits are moved to a separate file,
the SMP alternatives code is added there.
* The patch adds some new elf sections to the kernel:
.smp_altinstructions
like .altinstructions, also contains a list
of alt_instr structs.
.smp_altinstr_replacement
like .altinstr_replacement, but also has some space to
save original instruction before replaving it.
.smp_locks
list of pointers to lock prefixes which can be nop'ed
out on UP.
The first two are used to replace more complex instruction
sequences such as spinlocks and semaphores. It would be possible
to deal with the lock prefixes with that as well, but by handling
them as special case the table sizes become much smaller.
* The sections are page-aligned and padded up to page size, so they
can be free if they are not needed.
* Splitted the code to release init pages to a separate function and
use it to release the elf sections if they are unused.
please apply,
Gerd
Attached Files:
-
smp-alternatives-40.diff (35.9 KB)