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Date: Fri, 4 Feb 2022 15:39:02 -0800 From: "Paul E. McKenney" <paulmck@...nel.org> To: rcu@...r.kernel.org Cc: linux-kernel@...r.kernel.org, kernel-team@...com, rostedt@...dmis.org, "Paul E. McKenney" <paulmck@...nel.org> Subject: [PATCH rcu 19/19] srcu: Add contention check to call_srcu() srcu_data ->lock acquisition This commit increases the sensitivity of contention detection by adding checks to the acquisition of the srcu_data structure's lock on the call_srcu() code path. Signed-off-by: Paul E. McKenney <paulmck@...nel.org> --- kernel/rcu/srcutree.c | 45 ++++++++++++++++++++++++++++++++++--------- 1 file changed, 36 insertions(+), 9 deletions(-) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index c3968e091d019..31a7a9e2445da 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -320,18 +320,13 @@ static void srcu_transition_to_big(struct srcu_struct *ssp) } /* - * Acquire the specified srcu_struct structure's ->lock, but check for - * excessive contention, which results in initiation of a transition - * to SRCU_SIZE_BIG. But only if the srcutree.convert_to_big module - * parameter permits this. + * Check to see if the just-encountered contention event justifies + * a transition to SRCU_SIZE_BIG. */ -static void spin_lock_irqsave_ssp_contention(struct srcu_struct *ssp, unsigned long *flags) +static void spin_lock_irqsave_check_contention(struct srcu_struct *ssp) { unsigned long j; - if (spin_trylock_irqsave_rcu_node(ssp, *flags)) - return; - spin_lock_irqsave_rcu_node(ssp, *flags); if (!SRCU_SIZING_IS_CONTEND() || ssp->srcu_size_state) return; j = jiffies; @@ -344,6 +339,38 @@ static void spin_lock_irqsave_ssp_contention(struct srcu_struct *ssp, unsigned l __srcu_transition_to_big(ssp); } +/* + * Acquire the specified srcu_data structure's ->lock, but check for + * excessive contention, which results in initiation of a transition + * to SRCU_SIZE_BIG. But only if the srcutree.convert_to_big module + * parameter permits this. + */ +static void spin_lock_irqsave_sdp_contention(struct srcu_data *sdp, unsigned long *flags) +{ + struct srcu_struct *ssp = sdp->ssp; + + if (spin_trylock_irqsave_rcu_node(sdp, *flags)) + return; + spin_lock_irqsave_rcu_node(ssp, *flags); + spin_lock_irqsave_check_contention(ssp); + spin_unlock_irqrestore_rcu_node(ssp, *flags); + spin_lock_irqsave_rcu_node(sdp, *flags); +} + +/* + * Acquire the specified srcu_struct structure's ->lock, but check for + * excessive contention, which results in initiation of a transition + * to SRCU_SIZE_BIG. But only if the srcutree.convert_to_big module + * parameter permits this. + */ +static void spin_lock_irqsave_ssp_contention(struct srcu_struct *ssp, unsigned long *flags) +{ + if (spin_trylock_irqsave_rcu_node(ssp, *flags)) + return; + spin_lock_irqsave_rcu_node(ssp, *flags); + spin_lock_irqsave_check_contention(ssp); +} + /* * First-use initialization of statically allocated srcu_struct * structure. Wiring up the combining tree is more than can be @@ -989,7 +1016,7 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp, } else { sdp = raw_cpu_ptr(ssp->sda); } - spin_lock_irqsave_rcu_node(sdp, flags); + spin_lock_irqsave_sdp_contention(sdp, &flags); if (rhp) rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp); rcu_segcblist_advance(&sdp->srcu_cblist, -- 2.31.1.189.g2e36527f23
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