From: Paolo Bonzini <pbonzini@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>, Alexander Graf <agraf@suse.de>
Cc: "Jim Mattson" <jmattson@google.com>,
"kvm list" <kvm@vger.kernel.org>,
"Radim Krčmář" <rkrcmar@redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
"Gabriel L. Somlo" <gsomlo@gmail.com>,
"Jonathan Corbet" <corbet@lwn.net>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>,
"H. Peter Anvin" <hpa@zytor.com>,
"the arch/x86 maintainers" <x86@kernel.org>,
"Joerg Roedel" <joro@8bytes.org>,
linux-doc@vger.kernel.org, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH v6] kvm: better MWAIT emulation for guests
Date: Fri, 21 Apr 2017 12:02:53 +0200 [thread overview]
Message-ID: <f1046a02-d42d-0b0b-47e0-f1055788a13b@redhat.com> (raw)
In-Reply-To: <20170412185249-mutt-send-email-mst@kernel.org>
On 12/04/2017 18:29, Michael S. Tsirkin wrote:
> I don't really agree we do not need the PV flag. mwait on kvm is
> different from mwait on bare metal in that you are heavily penalized by
> scheduler for polling unless you configure the host just so.
> HLT lets you give up the host CPU if you know you won't need
> it for a long time.
>
> So while many people can get by with monitor cpuid (those that isolate
> host CPUs) and it's a valuable option to have, I think a PV flag is also
> a valuable option and can be set for more configurations.
>
> Guest has an idle driver calling mwait on short waits and halt on longer
> ones. I'm in fact testing an idle driver using such a PV flag and will
> post when ready (after vacation ~3 weeks from now probably).
For now I think I'm removing the PV flag, making this just an
optimization of commit 87c00572ba05aa8c ("kvm: x86: emulate
monitor and mwait instructions as nop").
We can add it for 4.13 together with the idle driver.
Paolo
next prev parent reply other threads:[~2017-04-21 10:03 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-11 11:45 [Qemu-devel] [PATCH v6] kvm: better MWAIT emulation for guests Alexander Graf
2017-04-11 12:41 ` Gabriel L. Somlo
2017-04-11 12:43 ` Gabriel L. Somlo
2017-04-11 12:43 ` Alexander Graf
2017-04-11 17:10 ` Jim Mattson
2017-04-11 18:23 ` Alexander Graf
2017-04-12 14:34 ` Jim Mattson
2017-04-12 14:54 ` Alexander Graf
2017-04-12 15:20 ` Jim Mattson
2017-04-12 16:29 ` Michael S. Tsirkin
2017-04-21 10:02 ` Paolo Bonzini [this message]
2017-04-21 10:05 ` Alexander Graf
2017-04-21 10:06 ` Paolo Bonzini
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