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| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2017-01-27 14:17:50 -0800 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2017-04-18 11:38:18 -0700 |
| commit | 9226b10d78ffe7895549045fe388dc5e73b87eac (patch) | |
| tree | 29d959a37f8d502c97948e49f895ae3269793b12 /Documentation/RCU | |
| parent | 0f9be8cabbc343218dd2807af7308656be113045 (diff) | |
| download | lwn-9226b10d78ffe7895549045fe388dc5e73b87eac.tar.gz lwn-9226b10d78ffe7895549045fe388dc5e73b87eac.zip | |
rcu: Place guard on rcu_all_qs() and rcu_note_context_switch() actions
The rcu_all_qs() and rcu_note_context_switch() do a series of checks,
taking various actions to supply RCU with quiescent states, depending
on the outcomes of the various checks. This is a bit much for scheduling
fastpaths, so this commit creates a separate ->rcu_urgent_qs field in
the rcu_dynticks structure that acts as a global guard for these checks.
Thus, in the common case, rcu_all_qs() and rcu_note_context_switch()
check the ->rcu_urgent_qs field, find it false, and simply return.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Diffstat (limited to 'Documentation/RCU')
| -rw-r--r-- | Documentation/RCU/Design/Data-Structures/Data-Structures.html | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.html b/Documentation/RCU/Design/Data-Structures/Data-Structures.html index e4bf20a68fa3..4dec89097559 100644 --- a/Documentation/RCU/Design/Data-Structures/Data-Structures.html +++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.html @@ -1106,6 +1106,7 @@ Its fields are as follows: 3 atomic_t dynticks; 4 bool rcu_need_heavy_qs; 5 unsigned long rcu_qs_ctr; + 6 bool rcu_urgent_qs; </pre> <p>The <tt>->dynticks_nesting</tt> field counts the @@ -1131,12 +1132,20 @@ it is willing to call for heavy-weight dyntick-counter operations. This flag is checked by RCU's context-switch and <tt>cond_resched()</tt> code, which provide a momentary idle sojourn in response. -</p><p>Finally the <tt>->rcu_qs_ctr</tt> field is used to record +</p><p>The <tt>->rcu_qs_ctr</tt> field is used to record quiescent states from <tt>cond_resched()</tt>. Because <tt>cond_resched()</tt> can execute quite frequently, this must be quite lightweight, as in a non-atomic increment of this per-CPU field. +</p><p>Finally, the <tt>->rcu_urgent_qs</tt> field is used to record +the fact that the RCU core code would really like to see a quiescent +state from the corresponding CPU, with the various other fields indicating +just how badly RCU wants this quiescent state. +This flag is checked by RCU's context-switch and <tt>cond_resched()</tt> +code, which, if nothing else, non-atomically increment <tt>->rcu_qs_ctr</tt> +in response. + <table> <tr><th> </th></tr> <tr><th align="left">Quick Quiz:</th></tr> |