linux-kernel - [RESEND PATCH 2/3] arch/powerpc/kvm: Optimize the server number -> ICP lookup

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Message-ID: <20240520082014.140697-3-gautam@linux.ibm.com>
Date: Mon, 20 May 2024 13:50:09 +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, clg@...d.org
Cc: Gautam Menghani <gautam@...ux.ibm.com>, linuxppc-dev@...ts.ozlabs.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RESEND PATCH 2/3] arch/powerpc/kvm: Optimize the server number -> ICP lookup

Given a server number, kvmppc_xics_find_server() does a linear search
over the vcpus of a VM. Optimize this logic by using an array to
maintain the mapping between server number -> icp.

Signed-off-by: Gautam Menghani <gautam@...ux.ibm.com>
---
 arch/powerpc/kvm/book3s_xics.c |  4 ++--
 arch/powerpc/kvm/book3s_xics.h | 10 ++--------
 2 files changed, 4 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_xics.c b/arch/powerpc/kvm/book3s_xics.c
index 12de526f04c4..1dc2f77571e7 100644
--- a/arch/powerpc/kvm/book3s_xics.c
+++ b/arch/powerpc/kvm/book3s_xics.c
@@ -47,8 +47,6 @@
  * TODO
  * ====
  *
- * - Speed up server# -> ICP lookup (array ? hash table ?)
- *
  * - Make ICS lockless as well, or at least a per-interrupt lock or hashed
  *   locks array to improve scalability
  */
@@ -1062,6 +1060,7 @@ static struct kvmppc_ics *kvmppc_xics_create_ics(struct kvm *kvm,
 static int kvmppc_xics_create_icp(struct kvm_vcpu *vcpu, unsigned long server_num)
 {
 	struct kvmppc_icp *icp;
+	struct kvm *kvm = vcpu->kvm;
 
 	if (!vcpu->kvm->arch.xics)
 		return -ENODEV;
@@ -1078,6 +1077,7 @@ static int kvmppc_xics_create_icp(struct kvm_vcpu *vcpu, unsigned long server_nu
 	icp->state.mfrr = MASKED;
 	icp->state.pending_pri = MASKED;
 	vcpu->arch.icp = icp;
+	kvm->arch.xics->icps[server_num] = icp;
 
 	XICS_DBG("created server for vcpu %d\n", vcpu->vcpu_id);
 
diff --git a/arch/powerpc/kvm/book3s_xics.h b/arch/powerpc/kvm/book3s_xics.h
index 8fcb34ea47a4..feeb0897d555 100644
--- a/arch/powerpc/kvm/book3s_xics.h
+++ b/arch/powerpc/kvm/book3s_xics.h
@@ -111,19 +111,13 @@ struct kvmppc_xics {
 	u32 err_noics;
 	u32 err_noicp;
 	struct kvmppc_ics *ics[KVMPPC_XICS_MAX_ICS_ID + 1];
+	DECLARE_FLEX_ARRAY(struct kvmppc_icp *, icps);
 };
 
 static inline struct kvmppc_icp *kvmppc_xics_find_server(struct kvm *kvm,
 							 u32 nr)
 {
-	struct kvm_vcpu *vcpu = NULL;
-	unsigned long i;
-
-	kvm_for_each_vcpu(i, vcpu, kvm) {
-		if (vcpu->arch.icp && nr == vcpu->arch.icp->server_num)
-			return vcpu->arch.icp;
-	}
-	return NULL;
+	return kvm->arch.xics->icps[nr];
 }
 
 static inline struct kvmppc_ics *kvmppc_xics_find_ics(struct kvmppc_xics *xics,
-- 
2.44.0