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padata: update API documentation

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Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
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Steffen Klassert 2010-07-27 07:20:47 +02:00 committed by Herbert Xu
parent 0500e9b3f1
commit 313910d3b9
1 changed files with 64 additions and 12 deletions
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76
Documentation/padata.txt
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@ -1,5 +1,5 @@
The padata parallel execution mechanism
Last updated for 2.6.34
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
@ -13,12 +13,28 @@ overall control of how tasks are to be run:
#include <linux/padata.h>
struct padata_instance *padata_alloc(const struct cpumask *cpumask,
struct workqueue_struct *wq);
struct padata_instance *padata_alloc(struct workqueue_struct *wq,
const struct cpumask *pcpumask,
const struct cpumask *cbcpumask);
The cpumask describes which processors will be used to execute work
submitted to this instance. The workqueue wq is where the work will
actually be done; it should be a multithreaded queue, naturally.
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.
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:
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
is going to use it.
There are functions for enabling and disabling the instance:
@ -34,13 +50,49 @@ is unused.
The list of CPUs to be used can be adjusted with these functions:
int padata_set_cpumask(struct padata_instance *pinst,
int padata_set_cpumasks(struct padata_instance *pinst,
cpumask_var_t pcpumask,
cpumask_var_t cbcpumask);
int padata_set_cpumask(struct padata_instance *pinst, int cpumask_type,
cpumask_var_t cpumask);
int padata_add_cpu(struct padata_instance *pinst, int cpu);
int padata_remove_cpu(struct padata_instance *pinst, int cpu);
int padata_add_cpu(struct padata_instance *pinst, int cpu, int mask);
int padata_remove_cpu(struct padata_instance *pinst, int cpu, int mask);
Changing the CPU mask has the look of an expensive operation, though, so it
probably should not be done with great frequency.
Changing the CPU masks are expensive operations, though, so it should not be
done with great frequency.
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
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
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:
int padata_register_cpumask_notifier(struct padata_instance *pinst,
struct notifier_block *nblock);
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.
Padata calls the notifier chain with:
blocking_notifier_call_chain(&pinst->cpumask_change_notifier,
notification_mask,
&pd_new->cpumask);
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.
Actually submitting work to the padata instance requires the creation of a
padata_priv structure:
@ -53,7 +105,7 @@ padata_priv structure:
This structure will almost certainly be embedded within some larger
structure specific to the work to be done. Most its fields are private to
padata, but the structure should be zeroed at initialization time, and the
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.