linux-kernel - [PATCH] KVM: PPC: BOOK3S: book3s_hv_nested.c: improve branch prediction for k.alloc

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Date:   Fri,  7 Apr 2023 05:31:47 -0400
From:   Kautuk Consul <kconsul@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Fabiano Rosas <farosas@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Chao Peng <chao.p.peng@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Kautuk Consul <kconsul@...ux.vnet.ibm.com>
Subject: [PATCH] KVM: PPC: BOOK3S: book3s_hv_nested.c: improve branch prediction for k.alloc

I used the unlikely() macro on the return values of the k.alloc
calls and found that it changes the code generation a bit.
Optimize all return paths of k.alloc calls by improving
branch prediction on return value of k.alloc.

Signed-off-by: Kautuk Consul <kconsul@...ux.vnet.ibm.com>
---
 arch/powerpc/kvm/book3s_hv_nested.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv_nested.c b/arch/powerpc/kvm/book3s_hv_nested.c
index 5a64a1341e6f..dbf2dd073e1f 100644
--- a/arch/powerpc/kvm/book3s_hv_nested.c
+++ b/arch/powerpc/kvm/book3s_hv_nested.c
@@ -446,7 +446,7 @@ long kvmhv_nested_init(void)
 		ptb_order = 12;
 	pseries_partition_tb = kmalloc(sizeof(struct patb_entry) << ptb_order,
 				       GFP_KERNEL);
-	if (!pseries_partition_tb) {
+	if (unlikely(!pseries_partition_tb)) {
 		pr_err("kvm-hv: failed to allocated nested partition table\n");
 		return -ENOMEM;
 	}
@@ -575,7 +575,7 @@ long kvmhv_copy_tofrom_guest_nested(struct kvm_vcpu *vcpu)
 		return H_PARAMETER;
 
 	buf = kzalloc(n, GFP_KERNEL | __GFP_NOWARN);
-	if (!buf)
+	if (unlikely(!buf))
 		return H_NO_MEM;
 
 	gp = kvmhv_get_nested(vcpu->kvm, l1_lpid, false);
@@ -689,7 +689,7 @@ static struct kvm_nested_guest *kvmhv_alloc_nested(struct kvm *kvm, unsigned int
 	long shadow_lpid;
 
 	gp = kzalloc(sizeof(*gp), GFP_KERNEL);
-	if (!gp)
+	if (unlikely(!gp))
 		return NULL;
 	gp->l1_host = kvm;
 	gp->l1_lpid = lpid;
@@ -1633,7 +1633,7 @@ static long int __kvmhv_nested_page_fault(struct kvm_vcpu *vcpu,
 	/* 4. Insert the pte into our shadow_pgtable */
 
 	n_rmap = kzalloc(sizeof(*n_rmap), GFP_KERNEL);
-	if (!n_rmap)
+	if (unlikely(!n_rmap))
 		return RESUME_GUEST; /* Let the guest try again */
 	n_rmap->rmap = (n_gpa & RMAP_NESTED_GPA_MASK) |
 		(((unsigned long) gp->l1_lpid) << RMAP_NESTED_LPID_SHIFT);
-- 
2.39.2