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author | Ingo Molnar <mingo@kernel.org> | 2017-11-02 10:57:24 +0100 |
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committer | Ingo Molnar <mingo@kernel.org> | 2017-11-02 10:57:24 +0100 |
commit | 3357b0d3c7323d73806571192e9f633bb6ba3d54 (patch) | |
tree | a92fb225bfdda901783ad662a1fea0baddfb81e1 /include/linux/swait.h | |
parent | 82c62fa0c49aa305104013cee4468772799bb391 (diff) | |
parent | e27c310af5c05cf876d9cad006928076c27f54d4 (diff) | |
download | linux-3357b0d3c7323d73806571192e9f633bb6ba3d54.tar.gz linux-3357b0d3c7323d73806571192e9f633bb6ba3d54.tar.bz2 linux-3357b0d3c7323d73806571192e9f633bb6ba3d54.zip |
Merge branch 'x86/mpx/prep' into x86/asm
Pick up some of the MPX commits that modify the syscall entry code,
to have a common base and to reduce conflicts.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'include/linux/swait.h')
-rw-r--r-- | include/linux/swait.h | 27 |
1 files changed, 16 insertions, 11 deletions
diff --git a/include/linux/swait.h b/include/linux/swait.h index 73e97a08d3d0..cf30f5022472 100644 --- a/include/linux/swait.h +++ b/include/linux/swait.h @@ -9,13 +9,16 @@ /* * Simple wait queues * - * While these are very similar to the other/complex wait queues (wait.h) the - * most important difference is that the simple waitqueue allows for - * deterministic behaviour -- IOW it has strictly bounded IRQ and lock hold - * times. + * While these are very similar to regular wait queues (wait.h) the most + * important difference is that the simple waitqueue allows for deterministic + * behaviour -- IOW it has strictly bounded IRQ and lock hold times. * - * In order to make this so, we had to drop a fair number of features of the - * other waitqueue code; notably: + * Mainly, this is accomplished by two things. Firstly not allowing swake_up_all + * from IRQ disabled, and dropping the lock upon every wakeup, giving a higher + * priority task a chance to run. + * + * Secondly, we had to drop a fair number of features of the other waitqueue + * code; notably: * * - mixing INTERRUPTIBLE and UNINTERRUPTIBLE sleeps on the same waitqueue; * all wakeups are TASK_NORMAL in order to avoid O(n) lookups for the right @@ -24,12 +27,14 @@ * - the exclusive mode; because this requires preserving the list order * and this is hard. * - * - custom wake functions; because you cannot give any guarantees about - * random code. - * - * As a side effect of this; the data structures are slimmer. + * - custom wake callback functions; because you cannot give any guarantees + * about random code. This also allows swait to be used in RT, such that + * raw spinlock can be used for the swait queue head. * - * One would recommend using this wait queue where possible. + * As a side effect of these; the data structures are slimmer albeit more ad-hoc. + * For all the above, note that simple wait queues should _only_ be used under + * very specific realtime constraints -- it is best to stick with the regular + * wait queues in most cases. */ struct task_struct; |