ACE, is an acronym for Atomic Code Execution and provides spin_lock_irqsave and spin_lock_irqrestore semantics in user space.
Signed-off-by: Wink Saville <[EMAIL PROTECTED]> --- Documentation/ace.txt | 100 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 100 insertions(+), 0 deletions(-) create mode 100644 Documentation/ace.txt Index: linux-2.6/Documentation/ace.txt =================================================================== --- /dev/null 1970-01-01 00:00:00.000000000 +0000 +++ linux-2.6/Documentation/ace.txt 2007-04-29 21:52:04.000000000 -0700 @@ -0,0 +1,100 @@ +Title : Atomic Code Execution (ACE) +Authors : Wink Saville <[EMAIL PROTECTED]> + +CONTENTS + +1. Concepts +2. Architectures Supported +3. Configuring +4. API Reference +5. TODO + + +1. Concepts + +Atomic Code Execution (ACE) allows code to execute as if it was +surrounded by spin_lock_irqsave and spin_unlock_irqrestore without +requiring actual access to the processor flags register. Thus code +executing within the ACE area can also be executed from user space or +kernel space. This is accomplished by using spin locks when executing +within the ACE area and changes to arch/x86_64/kernel/entry.S such that +when an interrupt occurs while executing code in the ACE area that code +will be completed before the interrupt is dispatched. + +The modifications to entry.S starts at the label ace_common plus the +macro HANDLE_ACE immediately following. HANDLE_ACE invokes ace_common +at the beginning of each interrupt, if it finds that code in the ACE +area was interrupted it causes the ACE code to resume execution prior +to handling the interrupt. + +The code for the ACE area is in the file arch/x86_64/kernel/ace.S. This +file contains all of the code that maybe executed by the kernel or +user-space. To be able to share this code with user space the code is +also compiled by user space, but this is only to generate the jump +table. Other techniques are possible, but this is the current +implementation and can be seen in the directory test/ace. + +The implementation of the code in the ACE area must be coordinated with +how the code in HANDLE_ACE is implemented and will be specific to each +architecture. The primary requirement is that it must be easy for the +ISR code to continue execution and it must be easy for both user and +kernel code to execute it. To make it simple to continue execution the +ISR code alters the ACE code return address. + +This is done by having the ACE code always return to the non-ACE code +via register r11. This allows the HANDLE_ACE code to swap the contents +of r11 with the interrupted address and thus compete the ACE code which +will release the spinlock and the original caller will be returned to +when the ISR completes. Thus giving us the semantic that ACE area code +was executed as if it was surrounded by a spin_lock_irqsave and a +spin_unlock_irqrestore. + +To allow the above algorithm to work under all circumstances the ACE +area code must appear in every user and kernel thread, this is +accomplished by allocting the ACE area using kshmem_alloc_at. + +The ACE area is initialized by calling +drivers/ace/ace_device.c/ace_init() from init/main.c/start_kernel(). + + +2. Architectures Supported + +- X86_64 + + +3. Configuring + +In "Processor type and features" select "Atomic Code Execution (ACE)". + + +4. ACE area API Reference + +ACE supports the following API: + +uint64_t ace_inc_counter(void) + + Increment the counter + + +uint64_t ace_inc_timer_counter(void) + + Increment the timer counter + + +void ace_get_counters(uint64_t *counter, uint64_t *timer_counter) + + Return the counter and timer counter + + +5. ACE device driver API Reference + +The ACE driver must be opened before accessing any of the ACE are API +routines and close upon exiting. The driver name is /dev/ace. +Currently there is an ioctl routine but no operations are defined. + + +5. TODO + +a. Decide how to handle page faults while executing ACE. +b. Decide upon the actual code needed in ACE. + ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
