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srcu: Rename srcu_might_be_idle() to srcu_should_expedite()

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SRCU auto-expedites grace periods that follow a sufficiently long idle
period, and the srcu_might_be_idle() function is used to make this
decision.  However, the upcoming light-weight SRCU readers will not do
auto-expediting because doing so would cause the grace-period machinery
to invoke synchronize_rcu_expedited() twice, with IPIs all around.
However, software-engineering considerations force this determination
to remain in srcu_might_be_idle().

This commit therefore changes the name of srcu_might_be_idle() to
srcu_should_expedite(), thus moving from what it currently does to why
it does it, this latter being more future-proof.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: <bpf@vger.kernel.org>
Reviewed-by: Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
This commit is contained in:
Paul E. McKenney 2024-10-15 09:10:58 -07:00 committed by Frederic Weisbecker
parent 79a20a8570
commit 5bc455ff25
1 changed files with 9 additions and 7 deletions
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16
kernel/rcu/srcutree.c
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@ -1139,7 +1139,8 @@ static void srcu_flip(struct srcu_struct *ssp)
}
/*
* If SRCU is likely idle, return true, otherwise return false.
* If SRCU is likely idle, in other words, the next SRCU grace period
* should be expedited, return true, otherwise return false.
*
* Note that it is OK for several current from-idle requests for a new
* grace period from idle to specify expediting because they will all end
@ -1159,7 +1160,7 @@ static void srcu_flip(struct srcu_struct *ssp)
* negligible when amortized over that time period, and the extra latency
* of a needlessly non-expedited grace period is similarly negligible.
*/
static bool srcu_might_be_idle(struct srcu_struct *ssp)
static bool srcu_should_expedite(struct srcu_struct *ssp)
{
unsigned long curseq;
unsigned long flags;
@ -1469,14 +1470,15 @@ EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
* Implementation of these memory-ordering guarantees is similar to
* that of synchronize_rcu().
*
* If SRCU is likely idle, expedite the first request. This semantic
* was provided by Classic SRCU, and is relied upon by its users, so TREE
* SRCU must also provide it. Note that detecting idleness is heuristic
* and subject to both false positives and negatives.
* If SRCU is likely idle as determined by srcu_should_expedite(),
* expedite the first request. This semantic was provided by Classic SRCU,
* and is relied upon by its users, so TREE SRCU must also provide it.
* Note that detecting idleness is heuristic and subject to both false
* positives and negatives.
*/
void synchronize_srcu(struct srcu_struct *ssp)
{
if (srcu_might_be_idle(ssp) || rcu_gp_is_expedited())
if (srcu_should_expedite(ssp) || rcu_gp_is_expedited())
synchronize_srcu_expedited(ssp);
else
__synchronize_srcu(ssp, true);