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rcu/segcblist: Add counters to segcblist datastructure

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Add counting of segment lengths of segmented callback list.

This will be useful for a number of things such as knowing how big the
ready-to-execute segment have gotten. The immediate benefit is ability
to trace how the callbacks in the segmented callback list change.

Also this patch remove hacks related to using donecbs's ->len field as a
temporary variable to save the segmented callback list's length. This cannot be
done anymore and is not needed.

Also fix SRCU:
The negative counting of the unsegmented list cannot be used to adjust
the segmented one. To fix this, sample the unsegmented length in
advance, and use it after CB execution to adjust the segmented list's
length.

Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Joel Fernandes (Google) 2020-09-23 11:22:09 -04:00 • committed by Paul E. McKenney
parent c2e13112e8
commit ae5c2341ed
4 changed files with 82 additions and 46 deletions
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5
kernel/rcu/srcutree.c
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@ -1160,6 +1160,7 @@ static void srcu_advance_state(struct srcu_struct *ssp)
*/
static void srcu_invoke_callbacks(struct work_struct *work)
{
long len;
bool more;
struct rcu_cblist ready_cbs;
struct rcu_head *rhp;
@ -1182,6 +1183,7 @@ static void srcu_invoke_callbacks(struct work_struct *work)
/* We are on the job! Extract and invoke ready callbacks. */
sdp->srcu_cblist_invoking = true;
rcu_segcblist_extract_done_cbs(&sdp->srcu_cblist, &ready_cbs);
len = ready_cbs.len;
spin_unlock_irq_rcu_node(sdp);
rhp = rcu_cblist_dequeue(&ready_cbs);
for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) {
@ -1190,13 +1192,14 @@ static void srcu_invoke_callbacks(struct work_struct *work)
rhp->func(rhp);
local_bh_enable();
}
WARN_ON_ONCE(ready_cbs.len);
/*
* Update counts, accelerate new callbacks, and if needed,
* schedule another round of callback invocation.
*/
spin_lock_irq_rcu_node(sdp);
rcu_segcblist_insert_count(&sdp->srcu_cblist, &ready_cbs);
rcu_segcblist_add_len(&sdp->srcu_cblist, -len);
(void)rcu_segcblist_accelerate(&sdp->srcu_cblist,
rcu_seq_snap(&ssp->srcu_gp_seq));
sdp->srcu_cblist_invoking = false;