linux-kernel - [PATCH 13/34] KVM: x86: hyper-v: optimize and cleanup kvm_hv_process

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Date:   Sat, 18 Nov 2023 07:50:44 -0800
From:   Yury Norov <yury.norov@...il.com>
To:     linux-kernel@...r.kernel.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org
Cc:     Yury Norov <yury.norov@...il.com>, Jan Kara <jack@...e.cz>,
        Mirsad Todorovac <mirsad.todorovac@....unizg.hr>,
        Matthew Wilcox <willy@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Maxim Kuvyrkov <maxim.kuvyrkov@...aro.org>,
        Alexey Klimov <klimov.linux@...il.com>
Subject: [PATCH 13/34] KVM: x86: hyper-v: optimize and cleanup kvm_hv_process_stimers()

The function traverses stimer_pending_bitmap n a for-loop bit by bit.
We can do it faster by using atomic find_and_set_bit().

While here, refactor the logic by decreasing indentation level
and dropping 2nd check for stimer->config.enable.

Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 arch/x86/kvm/hyperv.c | 39 +++++++++++++++++++--------------------
 1 file changed, 19 insertions(+), 20 deletions(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 238afd7335e4..460e300b558b 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -870,27 +870,26 @@ void kvm_hv_process_stimers(struct kvm_vcpu *vcpu)
 	if (!hv_vcpu)
 		return;
 
-	for (i = 0; i < ARRAY_SIZE(hv_vcpu->stimer); i++)
-		if (test_and_clear_bit(i, hv_vcpu->stimer_pending_bitmap)) {
-			stimer = &hv_vcpu->stimer[i];
-			if (stimer->config.enable) {
-				exp_time = stimer->exp_time;
-
-				if (exp_time) {
-					time_now =
-						get_time_ref_counter(vcpu->kvm);
-					if (time_now >= exp_time)
-						stimer_expiration(stimer);
-				}
-
-				if ((stimer->config.enable) &&
-				    stimer->count) {
-					if (!stimer->msg_pending)
-						stimer_start(stimer);
-				} else
-					stimer_cleanup(stimer);
-			}
+	for_each_test_and_clear_bit(i, hv_vcpu->stimer_pending_bitmap,
+					ARRAY_SIZE(hv_vcpu->stimer)) {
+		stimer = &hv_vcpu->stimer[i];
+		if (!stimer->config.enable)
+			continue;
+
+		exp_time = stimer->exp_time;
+
+		if (exp_time) {
+			time_now = get_time_ref_counter(vcpu->kvm);
+			if (time_now >= exp_time)
+				stimer_expiration(stimer);
 		}
+
+		if (stimer->count) {
+			if (!stimer->msg_pending)
+				stimer_start(stimer);
+		} else
+			stimer_cleanup(stimer);
+	}
 }
 
 void kvm_hv_vcpu_uninit(struct kvm_vcpu *vcpu)
-- 
2.39.2