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From: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
To: pbonzini@redhat.com, rkrcmar@redhat.com, agraf@suse.com, corbet@lwn.net
Cc: paulus@samba.org, mpe@ellerman.id.au, sam.bobroff@au1.ibm.com,
	kvm@vger.kernel.org, kvm-ppc@vger.kernel.org,
	linuxppc-dev@lists.ozlabs.org, benh@kernel.crashing.org,
	linux-doc@vger.kernel.org,
	Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Subject: [PATCH 4/6] powerpc/kvm: Decrease the powerpc default halt poll max value
Date: Fri, 14 Oct 2016 11:53:22 +1100	[thread overview]
Message-ID: <1476406404-32752-5-git-send-email-sjitindarsingh@gmail.com> (raw)
In-Reply-To: <1476406404-32752-1-git-send-email-sjitindarsingh@gmail.com>

KVM_HALT_POLL_NS_DEFAULT is an arch specific constant which sets the
default value of the halt_poll_ns kvm module parameter which determines
the global maximum halt polling interval.

The current value for powerpc is 500000 (500us) which means that any
repetitive workload with a period of less than that can drive the cpu
usage to 100% where it may have been mostly idle without halt polling.
This presents the possibility of a large increase in power usage with
a comparatively small performance benefit.

Reduce the default to 10000 (10us) and a user can tune this themselves
to set their affinity for halt polling based on the trade off between power
and performance which they are willing to make.

Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
---
 arch/powerpc/include/asm/kvm_host.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 28350a2..037b6a1 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -48,7 +48,7 @@
 #ifdef CONFIG_KVM_MMIO
 #define KVM_COALESCED_MMIO_PAGE_OFFSET 1
 #endif
-#define KVM_HALT_POLL_NS_DEFAULT 500000
+#define KVM_HALT_POLL_NS_DEFAULT 10000	/* 10 us */
 
 /* These values are internal and can be increased later */
 #define KVM_NR_IRQCHIPS          1
-- 
2.5.5

  parent reply	other threads:[~2016-10-14  0:54 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-10-14  0:53 [PATCH 0/6] kvm: powerpc halt polling updates Suraj Jitindar Singh
2016-10-14  0:53 ` [PATCH 1/6] kvm: export kvm module parameter variables Suraj Jitindar Singh
2016-10-14  0:53 ` [PATCH 2/6] powerpc/kvm: Use generic kvm module parameters in kvm-hv Suraj Jitindar Singh
2016-10-14  0:53 ` [PATCH 3/6] powerpc/kvm: Add check for module parameter halt_poll_ns Suraj Jitindar Singh
2016-10-14  0:53 ` Suraj Jitindar Singh [this message]
2016-10-14  0:53 ` [PATCH 5/6] powerpc/kvm: Comment style and print format fixups Suraj Jitindar Singh
2016-10-14  0:53 ` [PATCH 6/6] doc/kvm: Add halt polling documentation Suraj Jitindar Singh
2016-10-14  1:16   ` Wanpeng Li
2016-10-14  2:32     ` Suraj Jitindar Singh
2016-10-14  3:28 ` [PATCH 0/6] kvm: powerpc halt polling updates Sam Bobroff
2016-10-14  6:27 ` Nicholas Piggin

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