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Mon, 28 Feb 2022 06:22:35 +0000 From: Eugene Huang To: "qemu-devel@nongnu.org" Subject: Timer delays in VM Thread-Topic: Timer delays in VM Thread-Index: Adgsa5CaeBeekv16QLaiwwpCMOnvXw== Date: Mon, 28 Feb 2022 06:22:35 +0000 Message-ID: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nvidia.com; x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: 6862a138-2bed-4b51-62f1-08d9fa82b608 x-ms-traffictypediagnostic: BN6PR12MB1682:EE_ x-microsoft-antispam-prvs: x-ms-exchange-senderadcheck: 1 x-ms-exchange-antispam-relay: 0 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: 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 x-forefront-antispam-report: CIP:255.255.255.255; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable Hi, I am running qemu on an arm64 CentOS host. Inside a ubuntu VM, a process ru= ns a timer created using timer_t: ev.sigev_notify_function =3D m_callback; ... timer_create(CLOCK_MONOTONIC, &ev, &m_timer_t); This timer sometimes has significant delays. For example, the 50 ms timer c= an have a callback delay of 100ms. I did a host kernel trace and see a lot of WFx kvm_exits, and the followin= g events between kvm_exit and kvm_entry: kvm_exit kvm_wfx_arm64 kvm_get_timer_map sched_switch kvm_timer_save_state kvm_timer_update_irq vgic_update_irq_pending kvm_timer_restore_state kvm_vcpu_wakeup kvm_arm_setup_debug kvm_arm_set_dreg32 kvm_entry I have the following questions: 1. Why there are a lot WFx exits? Is the timer dependent on it? 2. Does this timer rely on kvm timer irq injection? 3. What can be any possible causes for the timer delay? Are there som= e locking mechanisms which can cause the delay? 4. What parameters can tune this timer? Thanks. --_000_BYAPR12MB3192248D73D9C8AF64076A62D9019BYAPR12MB3192namp_ Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Hi,

 

I am running qemu on an arm64 CentOS host. Inside a = ubuntu VM, a process runs a timer created using timer_t:

ev.sigev_notify_function =3D m_c= allback;

…

timer_create(CLOCK_MONOTONIC, &a= mp;ev, &m_timer_t);

 

This timer sometimes has significant delays. For exa= mple, the 50 ms timer can have a callback delay of 100ms.

 

I did a host kernel trace and see a lot of WFx kvm_e= xits, and  the following events between kvm_exit and kvm_entry:

kvm_exit<= /span>

kvm_wfx_arm64

kvm_get_timer_map

sched_switch

kvm_timer_save_state=

kvm_timer_update_irq=

vgic_update_irq_pend= ing

kvm_timer_restore_st= ate

kvm_vcpu_wakeup=

kvm_arm_setup_debug<= o:p>

kvm_arm_set_dreg32

kvm_entry=

 

I have the following questions:

1.     &= nbsp; Why there are a lot WFx exits? Is the timer depende= nt on it?

2.     &= nbsp; Does this timer rely on kvm timer irq injection?

3.     &= nbsp; What can be any possible causes for the timer delay= ? Are there some locking mechanisms which can cause the delay?

4.     &= nbsp; What parameters can tune this timer?

 

Thanks.

--_000_BYAPR12MB3192248D73D9C8AF64076A62D9019BYAPR12MB3192namp_--