From: Davidlohr Bueso <dave@stgolabs.net>
To: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
DanielWagnerwagi@monom.org, Boqun Feng <boqun.feng@gmail.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
Paul Gortmaker <paul.gortmaker@windriver.com>,
Ming Lei <ming.lei@redhat.com>, "Li, Yi" <yi1.li@linux.intel.com>,
"AKASHI, Takahiro" <takahiro.akashi@linaro.org>,
Jakub Kicinski <jakub.kicinski@netronome.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Petr Mladek <pmladek@suse.com>,
Andrew Lutomirski <luto@kernel.org>,
Kees Cook <keescook@chromium.org>,
David Howells <dhowells@redhat.com>,
Alan Cox <alan@linux.intel.com>, "Theodore Ts'o" <tytso@mit.edu>,
oss-drivers@netronome.com
Subject: Re: [PATCH] firmware: wake all waiters
Date: Thu, 29 Jun 2017 12:08:54 -0700 [thread overview]
Message-ID: <20170629190854.GE3954@linux-80c1.suse> (raw)
In-Reply-To: <20170627001534.GK21846@wotan.suse.de>
On Tue, 27 Jun 2017, Luis R. Rodriguez wrote:
> * As a side effect of this; the data structures are slimmer.
> *
>- * One would recommend using this wait queue where possible.
>+ * NOTE: swait is for cases of extreme memory considerations and some very
>+ * special realtime issues, where it saves a couple of bytes in structures that
>+ * need close packing. As such its very special-use. Consider using regular
>+ * waits queues from wait.h instead *first*.
How about the following?
diff --git a/include/linux/swait.h b/include/linux/swait.h
index 4a4e180d0a35..f72f274f2a5f 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;
next prev parent reply other threads:[~2017-06-29 19:09 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-23 23:37 [PATCH] firmware: wake all waiters Jakub Kicinski
2017-06-26 21:20 ` Luis R. Rodriguez
2017-06-26 21:23 ` [PATCH v2] firmware: fix batched requests - " Luis R. Rodriguez
2017-06-29 15:16 ` Greg KH
2017-06-29 15:17 ` Greg KH
2017-06-29 17:36 ` Luis R. Rodriguez
2017-06-26 23:41 ` [PATCH] firmware: " Luis R. Rodriguez
2017-06-27 2:10 ` Jakub Kicinski
2017-06-27 16:39 ` Luis R. Rodriguez
2017-06-27 21:25 ` Jakub Kicinski
2017-06-27 22:24 ` Luis R. Rodriguez
2017-06-27 22:39 ` Jakub Kicinski
2017-06-27 23:50 ` Luis R. Rodriguez
2017-06-28 7:06 ` [systemd-devel] " Lennart Poettering
2017-06-28 16:06 ` Luis R. Rodriguez
2017-06-28 16:21 ` Lennart Poettering
2017-06-28 17:57 ` Luis R. Rodriguez
2017-06-29 19:56 ` Daniel Wagner
2017-06-27 17:48 ` Bjorn Andersson
2017-06-27 18:03 ` Luis R. Rodriguez
2017-06-27 18:59 ` Bjorn Andersson
2017-06-27 19:08 ` Luis R. Rodriguez
2017-06-27 19:52 ` Bjorn Andersson
2017-06-27 20:24 ` Luis R. Rodriguez
2017-06-26 21:44 ` Linus Torvalds
2017-06-26 23:30 ` Luis R. Rodriguez
2017-06-26 23:43 ` Linus Torvalds
2017-06-27 0:15 ` Luis R. Rodriguez
2017-06-28 13:45 ` Davidlohr Bueso
2017-06-28 15:58 ` Luis R. Rodriguez
2017-06-28 19:03 ` Davidlohr Bueso
2017-06-29 19:08 ` Davidlohr Bueso [this message]
2017-06-29 19:48 ` Luis R. Rodriguez
2017-06-30 16:32 ` Davidlohr Bueso
2017-07-05 16:18 ` Peter Zijlstra
2017-07-05 16:33 ` Linus Torvalds
2017-07-12 18:45 ` Luis R. Rodriguez
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