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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2009-06-25 09:08:18 -0700
committerIngo Molnar <mingo@elte.hu>2009-07-03 10:02:29 +0200
commit240ebbf81f149b11a31e060ebe5ee51a3c775360 (patch)
treed8aa6601bd789991588e467bf734d40df36e1317 /Documentation/RCU/checklist.txt
parent0acc512cb1a29636df5e982c7d845edafe77c2d0 (diff)
downloadlinux-linaro-stable-240ebbf81f149b11a31e060ebe5ee51a3c775360.tar.gz
rcu: Add synchronize_sched_expedited() rcutorture doc + updates
This patch updates the rcutorture documentation to include updated output format. It also brings the RCU documentation up to date. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: akpm@linux-foundation.org Cc: torvalds@linux-foundation.org Cc: davem@davemloft.net Cc: dada1@cosmosbay.com Cc: zbr@ioremap.net Cc: jeff.chua.linux@gmail.com Cc: paulus@samba.org Cc: laijs@cn.fujitsu.com Cc: jengelh@medozas.de Cc: r000n@r000n.net Cc: benh@kernel.crashing.org Cc: mathieu.desnoyers@polymtl.ca LKML-Reference: <12459460983193-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'Documentation/RCU/checklist.txt')
-rw-r--r--Documentation/RCU/checklist.txt20
1 files changed, 15 insertions, 5 deletions
diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
index accfe2f5247d..51525a30e8b4 100644
--- a/Documentation/RCU/checklist.txt
+++ b/Documentation/RCU/checklist.txt
@@ -11,7 +11,10 @@ over a rather long period of time, but improvements are always welcome!
structure is updated more than about 10% of the time, then
you should strongly consider some other approach, unless
detailed performance measurements show that RCU is nonetheless
- the right tool for the job.
+ the right tool for the job. Yes, you might think of RCU
+ as simply cutting overhead off of the readers and imposing it
+ on the writers. That is exactly why normal uses of RCU will
+ do much more reading than updating.
Another exception is where performance is not an issue, and RCU
provides a simpler implementation. An example of this situation
@@ -240,10 +243,11 @@ over a rather long period of time, but improvements are always welcome!
instead need to use synchronize_irq() or synchronize_sched().
12. Any lock acquired by an RCU callback must be acquired elsewhere
- with irq disabled, e.g., via spin_lock_irqsave(). Failing to
- disable irq on a given acquisition of that lock will result in
- deadlock as soon as the RCU callback happens to interrupt that
- acquisition's critical section.
+ with softirq disabled, e.g., via spin_lock_irqsave(),
+ spin_lock_bh(), etc. Failing to disable irq on a given
+ acquisition of that lock will result in deadlock as soon as the
+ RCU callback happens to interrupt that acquisition's critical
+ section.
13. RCU callbacks can be and are executed in parallel. In many cases,
the callback code simply wrappers around kfree(), so that this
@@ -310,3 +314,9 @@ over a rather long period of time, but improvements are always welcome!
Because these primitives only wait for pre-existing readers,
it is the caller's responsibility to guarantee safety to
any subsequent readers.
+
+16. The various RCU read-side primitives do -not- contain memory
+ barriers. The CPU (and in some cases, the compiler) is free
+ to reorder code into and out of RCU read-side critical sections.
+ It is the responsibility of the RCU update-side primitives to
+ deal with this.