+=======================================
The padata parallel execution mechanism
-Last updated for 2.6.36
+=======================================
+
+:Last updated: for 2.6.36
Padata is a mechanism by which the kernel can farm work out to be done in
parallel on multiple CPUs while retaining the ordering of tasks. It was
sufficiently general fashion that it could be put to other uses as well.
The first step in using padata is to set up a padata_instance structure for
-overall control of how tasks are to be run:
+overall control of how tasks are to be run::
#include <linux/padata.h>
The pcpumask describes which processors will be used to execute work
submitted to this instance in parallel. The cbcpumask defines which
-processors are allowed to use as the serialization callback processor.
+processors are allowed to be used as the serialization callback processor.
The workqueue wq is where the work will actually be done; it should be
a multithreaded queue, naturally.
To allocate a padata instance with the cpu_possible_mask for both
-cpumasks this helper function can be used:
+cpumasks this helper function can be used::
struct padata_instance *padata_alloc_possible(struct workqueue_struct *wq);
Note: Padata maintains two kinds of cpumasks internally. The user supplied
cpumasks, submitted by padata_alloc/padata_alloc_possible and the 'usable'
-cpumasks. The usable cpumasks are always the subset of active cpus in the
-user supplied cpumasks, these are the cpumasks padata actually use. So
-it is legal to supply a cpumask to padata that contains offline cpus.
-Once a offline cpu in the user supplied cpumask comes online, padata
+cpumasks. The usable cpumasks are always a subset of active CPUs in the
+user supplied cpumasks; these are the cpumasks padata actually uses. So
+it is legal to supply a cpumask to padata that contains offline CPUs.
+Once an offline CPU in the user supplied cpumask comes online, padata
is going to use it.
-There are functions for enabling and disabling the instance:
+There are functions for enabling and disabling the instance::
int padata_start(struct padata_instance *pinst);
void padata_stop(struct padata_instance *pinst);
These functions are setting or clearing the "PADATA_INIT" flag;
if that flag is not set, other functions will refuse to work.
padata_start returns zero on success (flag set) or -EINVAL if the
-padata cpumask contains no active cpu (flag not set).
+padata cpumask contains no active CPU (flag not set).
padata_stop clears the flag and blocks until the padata instance
is unused.
-The list of CPUs to be used can be adjusted with these functions:
+The list of CPUs to be used can be adjusted with these functions::
int padata_set_cpumasks(struct padata_instance *pinst,
cpumask_var_t pcpumask,
It's possible to change both cpumasks of a padata instance with
padata_set_cpumasks by specifying the cpumasks for parallel execution (pcpumask)
-and for the serial callback function (cbcpumask). padata_set_cpumask is to
+and for the serial callback function (cbcpumask). padata_set_cpumask is used to
change just one of the cpumasks. Here cpumask_type is one of PADATA_CPU_SERIAL,
PADATA_CPU_PARALLEL and cpumask specifies the new cpumask to use.
-To simply add or remove one cpu from a certain cpumask the functions
-padata_add_cpu/padata_remove_cpu are used. cpu specifies the cpu to add or
+To simply add or remove one CPU from a certain cpumask the functions
+padata_add_cpu/padata_remove_cpu are used. cpu specifies the CPU to add or
remove and mask is one of PADATA_CPU_SERIAL, PADATA_CPU_PARALLEL.
If a user is interested in padata cpumask changes, he can register to
-the padata cpumask change notifier:
+the padata cpumask change notifier::
int padata_register_cpumask_notifier(struct padata_instance *pinst,
struct notifier_block *nblock);
-To unregister from that notifier:
+To unregister from that notifier::
int padata_unregister_cpumask_notifier(struct padata_instance *pinst,
struct notifier_block *nblock);
The padata cpumask change notifier notifies about changes of the usable
-cpumasks, i.e. the subset of active cpus in the user supplied cpumask.
+cpumasks, i.e. the subset of active CPUs in the user supplied cpumask.
-Padata calls the notifier chain with:
+Padata calls the notifier chain with::
blocking_notifier_call_chain(&pinst->cpumask_change_notifier,
notification_mask,
Here cpumask_change_notifier is registered notifier, notification_mask
is one of PADATA_CPU_SERIAL, PADATA_CPU_PARALLEL and cpumask is a pointer
-to a struct padata_cpumask that contains the new cpumask informations.
+to a struct padata_cpumask that contains the new cpumask information.
Actually submitting work to the padata instance requires the creation of a
-padata_priv structure:
+padata_priv structure::
struct padata_priv {
/* Other stuff here... */
};
This structure will almost certainly be embedded within some larger
-structure specific to the work to be done. Most its fields are private to
+structure specific to the work to be done. Most of its fields are private to
padata, but the structure should be zeroed at initialisation time, and the
parallel() and serial() functions should be provided. Those functions will
be called in the process of getting the work done as we will see
momentarily.
-The submission of work is done with:
+The submission of work is done with::
int padata_do_parallel(struct padata_instance *pinst,
struct padata_priv *padata, int cb_cpu);
outstanding, it should be prepared to be called again with a new job before
the previous one completes. When a task does complete, parallel() (or
whatever function actually finishes the job) should inform padata of the
-fact with a call to:
+fact with a call to::
void padata_do_serial(struct padata_priv *padata);
submitted.
The one remaining function in the padata API should be called to clean up
-when a padata instance is no longer needed:
+when a padata instance is no longer needed::
void padata_free(struct padata_instance *pinst);
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