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/* IBM_PROLOG_BEGIN_TAG */
/* This is an automatically generated prolog. */
/* */
/* $Source: src/include/kernel/deferred.H $ */
/* */
/* OpenPOWER HostBoot Project */
/* */
/* COPYRIGHT International Business Machines Corp. 2012,2014 */
/* */
/* Licensed under the Apache License, Version 2.0 (the "License"); */
/* you may not use this file except in compliance with the License. */
/* You may obtain a copy of the License at */
/* */
/* http://www.apache.org/licenses/LICENSE-2.0 */
/* */
/* Unless required by applicable law or agreed to in writing, software */
/* distributed under the License is distributed on an "AS IS" BASIS, */
/* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or */
/* implied. See the License for the specific language governing */
/* permissions and limitations under the License. */
/* */
/* IBM_PROLOG_END_TAG */
#ifndef __KERNEL_DEFERRED_H
#define __KERNEL_DEFERRED_H
/** @file deferred.H
* @brief Definition of kernel's deferred work constructs.
*
* These classes allow the kernel to synchronize all CPUs into kernel-mode
* and execute a task. These work items are queued up to be executed at
* the next time-slice expiration (decrementer exception).
*/
#include <kernel/types.h>
#include <kernel/spinlock.H>
#include <kernel/barrier.H>
/** @class DeferredWork
* @brief The base work-item type for deferred work.
*
* This class implements the synchronization and state transition for a
* general deferred work object. This class has methods for defining
* the behavior at specific points in its execution. A real behavior
* implementation should be defined by inheriting this class and overloading
* the desired virtual methods.
*
* The class is closely associated with the DeferredQueue, which is meant to
* hold pending DeferredWork objects. When a DeferredWork is complete it
* will remove itself from the DeferredQueue and self-delete.
*
* The state transition is as follows:
*
* <pre>
* MASTER Both NON-MASTER
* 1. Sync all
* 2. masterPreWork block
* 3. activeMainWork
* 4. Sync all
* 5. masterPostWork block
* 6. Last thread out deletes
* </pre>
*
* With the deferred work there is concern as to what to do with CPUs that
* come online while a deferred work item is being executed. For instance,
* the Heap Coalescing work could cause data integrity issues if a freshly
* activated CPU were to not block with the rest of the CPUs and instead
* started executed user-space code. To deal with this condition a
* CPU which is activated after the DeferredWork object was created will
* block at masterPreWork and masterPostWork stages and call
* nonactiveMainWork. Typically, the non-active CPUs perform no action
* but an implementation could assert for a race-condition that cannot
* be handled properly (though should never occur).
*/
class DeferredWork
{
public:
/** Default Constructor
* Initializes the work item and determines the CPU-activation
* sequence number at the time of creation.
*/
DeferredWork();
/** Default destructor
* Verifies that the work item has completed properly and is
* detached from the DeferredQueue.
*/
virtual ~DeferredWork();
/** Entry point for DeferredWork execution. */
void start();
protected:
// Functions to override for desired behavior:
/** Executed by master before "main" but after all active
* CPUs are sync'd.
*/
virtual void masterPreWork() {};
/** Executed by master after "main" work is complete. */
virtual void masterPostWork() {};
/** Executed by all [active] CPUs as the "main" work. */
virtual void activeMainWork() {};
/** Executed by all non-active CPUs as the "main" work. */
virtual void nonactiveMainWork() {};
private:
friend class DeferredQueue;
/** Barrier for synchronization of active CPUs. */
Barrier iv_barrier;
/** Count of CPUs in object and pointer to next object.
*
* Stored as "(cpu count << 32) | (DeferredWork* next)". This
* is done so that we can atomically check and/or set both
* values.
*/
volatile uint64_t iv_cpus_and_next;
/** Sequence ID at the time of creation. */
uint32_t iv_activeSeqId;
/** Boolean to indicate masterPreWork is complete. */
volatile bool iv_releasePre;
/** Boolean to indicate masterPostWork is complete. */
volatile bool iv_releasePost;
// Internal state transition functions.
void _waitForCpus();
void _masterPre();
void _waitAtPre();
void _masterPost();
void _waitAtPost();
void _cleanup();
};
/** @class DeferredQueue
* @brief Queue for DeferredWork objects.
*
* This class should have a Singleton instance for the whole kernel.
* Periodically, kernel threads can call the 'execute' function to execute
* pending work, if any is available. Additional work can be 'insert'ed.
*/
class DeferredQueue
{
public:
/** Default constructor. */
DeferredQueue();
/** Default destructor. */
~DeferredQueue();
/** Insert a work item into the queue.
*
* @param i_work - The item to add.
*
* Ownership of the work item is transfered to the queue, which is
* responsible for delete once the work is complete.
*/
static void insert(DeferredWork* i_work);
/** Execute any pending work items. */
static void execute();
private:
friend class DeferredWork;
// Instance functions for static pair.
void _insert(DeferredWork* i_work);
void _execute();
/** Remove a completed work item from the queue.
*
* This function is to be called by the master CPU executing the
* work item being completed.
*
* The work item is atomically removed from the queue and the
* count of CPUs with a pointer to the work item is compared
* against the count of CPUs in the work item. This function
* returns when all CPUs that have a pointer are actually inside
* the work item (so we can accurately determine when there is
* only a single CPU in the work item for delete).
*
* @param i_work - The item to remove.
*/
void _complete(DeferredWork* i_work);
/** Spinlock to protect insert / remove operations.
*
* This is effectively a "write" lock on the structure and all
* reads are done atomically. The writers have also use atomic
* update operations to ensure the readers (which are never
* locked) operate in a thread-safe manner.
*/
Spinlock lock;
/** Count of CPUs in first object and pointer to it.
*
* Stored as "(cpu count << 32) | (DeferredWork* ptr)". This
* is done so that we can atomically check and/or set both
* values.
*/
volatile uint64_t iv_cpus_and_next;
};
#endif
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