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author | Mauro Carvalho Chehab <mchehab@s-opensource.com> | 2017-05-14 13:35:29 -0300 |
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committer | Jonathan Corbet <corbet@lwn.net> | 2017-07-14 13:51:35 -0600 |
commit | db4df4819c8c3f7e749752cf95966034d4c42ed2 (patch) | |
tree | 86e40cbf7267904710b3c0b5f7191c7eda49b11f | |
parent | af7175bc21e3c2a73f85bc920852a136469c6112 (diff) | |
download | linux-db4df4819c8c3f7e749752cf95966034d4c42ed2.tar.bz2 |
futex-requeue-pi.txt: standardize document format
Each text file under Documentation follows a different
format. Some doesn't even have titles!
Change its representation to follow the adopted standard,
using ReST markups for it to be parseable by Sphinx:
- promote level for the document title;
- mark literal blocks.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
-rw-r--r-- | Documentation/futex-requeue-pi.txt | 93 |
1 files changed, 47 insertions, 46 deletions
diff --git a/Documentation/futex-requeue-pi.txt b/Documentation/futex-requeue-pi.txt index 77b36f59d16b..14ab5787b9a7 100644 --- a/Documentation/futex-requeue-pi.txt +++ b/Documentation/futex-requeue-pi.txt @@ -1,5 +1,6 @@ +================ Futex Requeue PI ----------------- +================ Requeueing of tasks from a non-PI futex to a PI futex requires special handling in order to ensure the underlying rt_mutex is never @@ -20,28 +21,28 @@ implementation would wake the highest-priority waiter, and leave the rest to the natural wakeup inherent in unlocking the mutex associated with the condvar. -Consider the simplified glibc calls: - -/* caller must lock mutex */ -pthread_cond_wait(cond, mutex) -{ - lock(cond->__data.__lock); - unlock(mutex); - do { - unlock(cond->__data.__lock); - futex_wait(cond->__data.__futex); - lock(cond->__data.__lock); - } while(...) - unlock(cond->__data.__lock); - lock(mutex); -} - -pthread_cond_broadcast(cond) -{ - lock(cond->__data.__lock); - unlock(cond->__data.__lock); - futex_requeue(cond->data.__futex, cond->mutex); -} +Consider the simplified glibc calls:: + + /* caller must lock mutex */ + pthread_cond_wait(cond, mutex) + { + lock(cond->__data.__lock); + unlock(mutex); + do { + unlock(cond->__data.__lock); + futex_wait(cond->__data.__futex); + lock(cond->__data.__lock); + } while(...) + unlock(cond->__data.__lock); + lock(mutex); + } + + pthread_cond_broadcast(cond) + { + lock(cond->__data.__lock); + unlock(cond->__data.__lock); + futex_requeue(cond->data.__futex, cond->mutex); + } Once pthread_cond_broadcast() requeues the tasks, the cond->mutex has waiters. Note that pthread_cond_wait() attempts to lock the @@ -53,29 +54,29 @@ In order to support PI-aware pthread_condvar's, the kernel needs to be able to requeue tasks to PI futexes. This support implies that upon a successful futex_wait system call, the caller would return to user space already holding the PI futex. The glibc implementation -would be modified as follows: - - -/* caller must lock mutex */ -pthread_cond_wait_pi(cond, mutex) -{ - lock(cond->__data.__lock); - unlock(mutex); - do { - unlock(cond->__data.__lock); - futex_wait_requeue_pi(cond->__data.__futex); - lock(cond->__data.__lock); - } while(...) - unlock(cond->__data.__lock); - /* the kernel acquired the mutex for us */ -} - -pthread_cond_broadcast_pi(cond) -{ - lock(cond->__data.__lock); - unlock(cond->__data.__lock); - futex_requeue_pi(cond->data.__futex, cond->mutex); -} +would be modified as follows:: + + + /* caller must lock mutex */ + pthread_cond_wait_pi(cond, mutex) + { + lock(cond->__data.__lock); + unlock(mutex); + do { + unlock(cond->__data.__lock); + futex_wait_requeue_pi(cond->__data.__futex); + lock(cond->__data.__lock); + } while(...) + unlock(cond->__data.__lock); + /* the kernel acquired the mutex for us */ + } + + pthread_cond_broadcast_pi(cond) + { + lock(cond->__data.__lock); + unlock(cond->__data.__lock); + futex_requeue_pi(cond->data.__futex, cond->mutex); + } The actual glibc implementation will likely test for PI and make the necessary changes inside the existing calls rather than creating new |