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Message-ID: <20240506161735.83358-4-gautam@linux.ibm.com>
Date: Mon, 6 May 2024 21:47:31 +0530
From: Gautam Menghani <gautam@...ux.ibm.com>
To: mpe@...erman.id.au, npiggin@...il.com, christophe.leroy@...roup.eu,
naveen.n.rao@...ux.ibm.com
Cc: Gautam Menghani <gautam@...ux.ibm.com>, linuxppc-dev@...ts.ozlabs.org,
kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] arch/powerpc/kvm: Reduce lock contention by moving spinlock from ics to irq_state
Take a spinlock on state of an IRQ instead of an entire ICS. This
improves scalability by reducing contention.
Signed-off-by: Gautam Menghani <gautam@...ux.ibm.com>
---
arch/powerpc/kvm/book3s_hv_rm_xics.c | 8 ++---
arch/powerpc/kvm/book3s_xics.c | 44 ++++++++++++----------------
arch/powerpc/kvm/book3s_xics.h | 2 +-
3 files changed, 23 insertions(+), 31 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_hv_rm_xics.c b/arch/powerpc/kvm/book3s_hv_rm_xics.c
index e42984878503..178bc869b519 100644
--- a/arch/powerpc/kvm/book3s_hv_rm_xics.c
+++ b/arch/powerpc/kvm/book3s_hv_rm_xics.c
@@ -308,7 +308,7 @@ static void icp_rm_deliver_irq(struct kvmppc_xics *xics, struct kvmppc_icp *icp,
state = &ics->irq_state[src];
/* Get a lock on the ICS */
- arch_spin_lock(&ics->lock);
+ arch_spin_lock(&state->lock);
/* Get our server */
if (!icp || state->server != icp->server_num) {
@@ -368,7 +368,7 @@ static void icp_rm_deliver_irq(struct kvmppc_xics *xics, struct kvmppc_icp *icp,
* Delivery was successful, did we reject somebody else ?
*/
if (reject && reject != XICS_IPI) {
- arch_spin_unlock(&ics->lock);
+ arch_spin_unlock(&state->lock);
icp->n_reject++;
new_irq = reject;
check_resend = 0;
@@ -397,13 +397,13 @@ static void icp_rm_deliver_irq(struct kvmppc_xics *xics, struct kvmppc_icp *icp,
smp_mb();
if (!icp->state.need_resend) {
state->resend = 0;
- arch_spin_unlock(&ics->lock);
+ arch_spin_unlock(&state->lock);
check_resend = 0;
goto again;
}
}
out:
- arch_spin_unlock(&ics->lock);
+ arch_spin_unlock(&state->lock);
}
static void icp_rm_down_cppr(struct kvmppc_xics *xics, struct kvmppc_icp *icp,
diff --git a/arch/powerpc/kvm/book3s_xics.c b/arch/powerpc/kvm/book3s_xics.c
index 1dc2f77571e7..466c92cf49fb 100644
--- a/arch/powerpc/kvm/book3s_xics.c
+++ b/arch/powerpc/kvm/book3s_xics.c
@@ -36,21 +36,13 @@
* LOCKING
* =======
*
- * Each ICS has a spin lock protecting the information about the IRQ
- * sources and avoiding simultaneous deliveries of the same interrupt.
+ * Each IRQ has a spin lock protecting its state sources and avoiding
+ * simultaneous deliveries of the same interrupt.
*
* ICP operations are done via a single compare & swap transaction
* (most ICP state fits in the union kvmppc_icp_state)
*/
-/*
- * TODO
- * ====
- *
- * - Make ICS lockless as well, or at least a per-interrupt lock or hashed
- * locks array to improve scalability
- */
-
/* -- ICS routines -- */
static void icp_deliver_irq(struct kvmppc_xics *xics, struct kvmppc_icp *icp,
@@ -142,7 +134,7 @@ static bool write_xive(struct kvmppc_xics *xics, struct kvmppc_ics *ics,
unsigned long flags;
local_irq_save(flags);
- arch_spin_lock(&ics->lock);
+ arch_spin_lock(&state->lock);
state->server = server;
state->priority = priority;
@@ -154,7 +146,7 @@ static bool write_xive(struct kvmppc_xics *xics, struct kvmppc_ics *ics,
deliver = true;
}
- arch_spin_unlock(&ics->lock);
+ arch_spin_unlock(&state->lock);
local_irq_restore(flags);
return deliver;
@@ -207,10 +199,10 @@ int kvmppc_xics_get_xive(struct kvm *kvm, u32 irq, u32 *server, u32 *priority)
state = &ics->irq_state[src];
local_irq_save(flags);
- arch_spin_lock(&ics->lock);
+ arch_spin_lock(&state->lock);
*server = state->server;
*priority = state->priority;
- arch_spin_unlock(&ics->lock);
+ arch_spin_unlock(&state->lock);
local_irq_restore(flags);
return 0;
@@ -406,7 +398,7 @@ static void icp_deliver_irq(struct kvmppc_xics *xics, struct kvmppc_icp *icp,
/* Get a lock on the ICS */
local_irq_save(flags);
- arch_spin_lock(&ics->lock);
+ arch_spin_lock(&state->lock);
/* Get our server */
if (!icp || state->server != icp->server_num) {
@@ -467,7 +459,7 @@ static void icp_deliver_irq(struct kvmppc_xics *xics, struct kvmppc_icp *icp,
* Delivery was successful, did we reject somebody else ?
*/
if (reject && reject != XICS_IPI) {
- arch_spin_unlock(&ics->lock);
+ arch_spin_unlock(&state->lock);
local_irq_restore(flags);
new_irq = reject;
check_resend = false;
@@ -497,14 +489,14 @@ static void icp_deliver_irq(struct kvmppc_xics *xics, struct kvmppc_icp *icp,
smp_mb();
if (!icp->state.need_resend) {
state->resend = 0;
- arch_spin_unlock(&ics->lock);
+ arch_spin_unlock(&state->lock);
local_irq_restore(flags);
check_resend = false;
goto again;
}
}
out:
- arch_spin_unlock(&ics->lock);
+ arch_spin_unlock(&state->lock);
local_irq_restore(flags);
}
@@ -992,20 +984,20 @@ static int xics_debug_show(struct seq_file *m, void *private)
seq_printf(m, "=========\nICS state for ICS 0x%x\n=========\n",
icsid);
- local_irq_save(flags);
- arch_spin_lock(&ics->lock);
for (i = 0; i < KVMPPC_XICS_IRQ_PER_ICS; i++) {
struct ics_irq_state *irq = &ics->irq_state[i];
+ local_irq_save(flags);
+ arch_spin_lock(&irq->lock);
seq_printf(m, "irq 0x%06x: server %#x prio %#x save prio %#x pq_state %d resend %d masked pending %d\n",
irq->number, irq->server, irq->priority,
irq->saved_priority, irq->pq_state,
irq->resend, irq->masked_pending);
+ arch_spin_unlock(&irq->lock);
+ local_irq_restore(flags);
}
- arch_spin_unlock(&ics->lock);
- local_irq_restore(flags);
}
return 0;
}
@@ -1189,7 +1181,7 @@ static int xics_get_source(struct kvmppc_xics *xics, long irq, u64 addr)
irqp = &ics->irq_state[idx];
local_irq_save(flags);
- arch_spin_lock(&ics->lock);
+ arch_spin_lock(&irqp->lock);
ret = -ENOENT;
if (irqp->exists) {
val = irqp->server;
@@ -1214,7 +1206,7 @@ static int xics_get_source(struct kvmppc_xics *xics, long irq, u64 addr)
ret = 0;
}
- arch_spin_unlock(&ics->lock);
+ arch_spin_unlock(&irqp->lock);
local_irq_restore(flags);
if (!ret && put_user(val, ubufp))
@@ -1254,7 +1246,7 @@ static int xics_set_source(struct kvmppc_xics *xics, long irq, u64 addr)
return -EINVAL;
local_irq_save(flags);
- arch_spin_lock(&ics->lock);
+ arch_spin_lock(&irqp->lock);
irqp->server = server;
irqp->saved_priority = prio;
if (val & KVM_XICS_MASKED)
@@ -1272,7 +1264,7 @@ static int xics_set_source(struct kvmppc_xics *xics, long irq, u64 addr)
if (val & KVM_XICS_QUEUED)
irqp->pq_state |= PQ_QUEUED;
irqp->exists = 1;
- arch_spin_unlock(&ics->lock);
+ arch_spin_unlock(&irqp->lock);
local_irq_restore(flags);
if (val & KVM_XICS_PENDING)
diff --git a/arch/powerpc/kvm/book3s_xics.h b/arch/powerpc/kvm/book3s_xics.h
index feeb0897d555..1ee62b7a8fdf 100644
--- a/arch/powerpc/kvm/book3s_xics.h
+++ b/arch/powerpc/kvm/book3s_xics.h
@@ -45,6 +45,7 @@ struct ics_irq_state {
u8 exists;
int intr_cpu;
u32 host_irq;
+ arch_spinlock_t lock;
};
/* Atomic ICP state, updated with a single compare & swap */
@@ -95,7 +96,6 @@ struct kvmppc_icp {
};
struct kvmppc_ics {
- arch_spinlock_t lock;
u16 icsid;
struct ics_irq_state irq_state[KVMPPC_XICS_IRQ_PER_ICS];
DECLARE_BITMAP(resend_map, KVMPPC_XICS_IRQ_PER_ICS);
--
2.44.0
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