linux-kernel - [PATCH 1/3] arch/powerpc/kvm: Use bitmap to speed up resend of irqs in ICS

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Date: Mon,  6 May 2024 21:47:29 +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 1/3] arch/powerpc/kvm: Use bitmap to speed up resend of irqs in ICS

When an irq is to be resent, all 1024 irqs in an ICS are scanned and the
irqs having 'resend' flag set are resent. Optimize this flow using bitmap
array to speed up the resends.

Signed-off-by: Gautam Menghani <gautam@...ux.ibm.com>
---
 arch/powerpc/kvm/book3s_xics.c | 22 +++++++++++-----------
 arch/powerpc/kvm/book3s_xics.h |  1 +
 2 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_xics.c b/arch/powerpc/kvm/book3s_xics.c
index 589a8f257120..12de526f04c4 100644
--- a/arch/powerpc/kvm/book3s_xics.c
+++ b/arch/powerpc/kvm/book3s_xics.c
@@ -47,9 +47,6 @@
  * TODO
  * ====
  *
- * - To speed up resends, keep a bitmap of "resend" set bits in the
- *   ICS
- *
  * - Speed up server# -> ICP lookup (array ? hash table ?)
  *
  * - Make ICS lockless as well, or at least a per-interrupt lock or hashed
@@ -125,15 +122,17 @@ static int ics_deliver_irq(struct kvmppc_xics *xics, u32 irq, u32 level)
 static void ics_check_resend(struct kvmppc_xics *xics, struct kvmppc_ics *ics,
 			     struct kvmppc_icp *icp)
 {
-	int i;
+	u32 irq;
+	struct ics_irq_state *state;
 
-	for (i = 0; i < KVMPPC_XICS_IRQ_PER_ICS; i++) {
-		struct ics_irq_state *state = &ics->irq_state[i];
-		if (state->resend) {
-			XICS_DBG("resend %#x prio %#x\n", state->number,
-				      state->priority);
-			icp_deliver_irq(xics, icp, state->number, true);
-		}
+	for_each_set_bit(irq, ics->resend_map, KVMPPC_XICS_IRQ_PER_ICS) {
+		state = &ics->irq_state[irq];
+
+		if (!test_and_clear_bit(irq, ics->resend_map))
+			continue;
+		if (!state)
+			continue;
+		icp_deliver_irq(xics, icp, state->number, true);
 	}
 }
 
@@ -489,6 +488,7 @@ static void icp_deliver_irq(struct kvmppc_xics *xics, struct kvmppc_icp *icp,
 		 */
 		smp_wmb();
 		set_bit(ics->icsid, icp->resend_map);
+		set_bit(src, ics->resend_map);
 
 		/*
 		 * If the need_resend flag got cleared in the ICP some time
diff --git a/arch/powerpc/kvm/book3s_xics.h b/arch/powerpc/kvm/book3s_xics.h
index 08fb0843faf5..8fcb34ea47a4 100644
--- a/arch/powerpc/kvm/book3s_xics.h
+++ b/arch/powerpc/kvm/book3s_xics.h
@@ -98,6 +98,7 @@ 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);
 };
 
 struct kvmppc_xics {
-- 
2.44.0