From: Paolo Bonzini <pbonzini@redhat.com>
To: David Matlack <dmatlack@google.com>,
Andy Lutomirski <luto@amacapital.net>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
X86 ML <x86@kernel.org>, kvm list <kvm@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Andrew Lutomirski <luto@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Eric Northup <digitaleric@google.com>
Subject: Re: [PATCH 1/1] KVM: don't allow irq_fpu_usable when the VCPU's XCR0 is loaded
Date: Mon, 14 Mar 2016 14:17:58 +0100 [thread overview]
Message-ID: <56E6BA06.7000907@redhat.com> (raw)
In-Reply-To: <CALzav=dRU9svdrF-CBKc_zfgz9ziAhJ8bkyPeMZV9T9jxOMdRg@mail.gmail.com>
On 11/03/2016 22:33, David Matlack wrote:
> > Is this better than just always keeping the host's XCR0 loaded outside
> > if the KVM interrupts-disabled region?
>
> Probably not. AFAICT KVM does not rely on it being loaded outside that
> region. xsetbv isn't insanely expensive, is it? Maybe to minimize the
> time spent with interrupts disabled it was put outside.
>
> I do like that your solution would be contained to KVM.
I agree with Andy. We do want a fix for recent kernels because of the
!eager_fpu case that Guangrong mentioned.
Paolo
ps: while Andy is planning to kill lazy FPU, I want to benchmark it with
KVM... Remember that with a single pre-xsave host in your cluster, your
virt management might happily default your VMs to a Westmere or Nehalem
CPU model. GCC might be a pretty good testbench for this (e.g. a kernel
compile with very high make -j), because outside of the lexer (which
plays SIMD games) it never uses the FPU.
next prev parent reply other threads:[~2016-03-14 13:18 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-11 20:47 [PATCH 0/1] KVM: x86: using the fpu in interrupt context with a guest's xcr0 David Matlack
2016-03-11 20:47 ` [PATCH 1/1] KVM: don't allow irq_fpu_usable when the VCPU's XCR0 is loaded David Matlack
2016-03-11 21:14 ` Andy Lutomirski
2016-03-11 21:33 ` David Matlack
2016-03-14 13:17 ` Paolo Bonzini [this message]
2016-03-15 18:27 ` Andy Lutomirski
2016-03-15 19:32 ` Paolo Bonzini
2016-03-16 3:55 ` Xiao Guangrong
2016-03-16 12:01 ` Paolo Bonzini
2016-03-14 7:46 ` [PATCH 0/1] KVM: x86: using the fpu in interrupt context with a guest's xcr0 Xiao Guangrong
2016-03-15 19:01 ` David Matlack
2016-03-16 3:43 ` Xiao Guangrong
2016-03-16 3:48 ` Andy Lutomirski
2016-03-16 17:11 ` David Matlack
2016-03-16 17:09 ` David Matlack
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=56E6BA06.7000907@redhat.com \
--to=pbonzini@redhat.com \
--cc=digitaleric@google.com \
--cc=dmatlack@google.com \
--cc=hpa@zytor.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@amacapital.net \
--cc=luto@kernel.org \
--cc=mingo@redhat.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).