linux-kernel - [PATCH v3] KVM: X86: Lower the default timer frequency limit to 200us

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Date:   Sat,  5 May 2018 04:02:32 -0700
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Anthoine Bourgeois <anthoine.bourgeois@...de-group.com>,
        Darren Kenny <darren.kenny@...cle.com>,
        Jan Kiszka <jan.kiszka@....de>
Subject: [PATCH v3] KVM: X86: Lower the default timer frequency limit to 200us

From: Wanpeng Li <wanpengli@...cent.com>

Anthoine reported:
 The period used by Windows change over time but it can be 1 
 milliseconds or less. I saw the limit_periodic_timer_frequency 
 print so 500 microseconds is sometimes reached.

As suggested by Paolo, lower the default timer frequency limit to a
smaller interval of 200 us (5000 Hz) to leave some headroom. This
is required due to Windows 10 changing the scheduler tick limit
from 1024 Hz to 2048 Hz.

Reported-by: Anthoine Bourgeois <anthoine.bourgeois@...de-group.com>
Suggested-by: Paolo Bonzini <pbonzini@...hat.com> 
Reviewed-by: Darren Kenny <darren.kenny@...cle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: Anthoine Bourgeois <anthoine.bourgeois@...de-group.com>
Cc: Darren Kenny <darren.kenny@...cle.com>
Cc: Jan Kiszka <jan.kiszka@....de>
Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
v2 -> v3:
 * update patch subject and description
v1 -> v2:
 * update patch subject and description

 arch/x86/kvm/x86.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 51ecd38..dc47073 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -114,7 +114,7 @@ module_param(ignore_msrs, bool, S_IRUGO | S_IWUSR);
 static bool __read_mostly report_ignored_msrs = true;
 module_param(report_ignored_msrs, bool, S_IRUGO | S_IWUSR);
 
-unsigned int min_timer_period_us = 500;
+unsigned int min_timer_period_us = 200;
 module_param(min_timer_period_us, uint, S_IRUGO | S_IWUSR);
 
 static bool __read_mostly kvmclock_periodic_sync = true;
-- 
2.7.4