From: Avi Kivity <avi@redhat.com>
To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: Re: [PATCH 04/19] qemu-kvm: x86: Drop MSR reset
Date: Thu, 05 May 2011 13:22:32 +0300 [thread overview]
Message-ID: <4DC27A68.3070409@redhat.com> (raw)
In-Reply-To: <4DC26EAA.7080803@siemens.com>
On 05/05/2011 12:32 PM, Jan Kiszka wrote:
> >> >
> >> > If the former, we simply do the reset operation per-cpu. It's the
> >> > natural thing anyway.
> >>
> >> Quite wasteful /wrt to memory given that the majority will be identical.
> >
> > We're talking a few hundred bytes per cpu. If you want to save memory,
> > look at the PhysPageDesc array, it takes up 0.4% of guest memory, so 4MB
> > for a 1GB guest.
>
> I know (that's fixable, BTW). But that should not excuse needless memory
> wasting elsewhere.
IMO a few hundred bytes is worth the correctness here.
> >
> >> >> Nevertheless, the qemu-kvm code is already unneeded today and can
> >> safely
> >> >> be removed IMHO.
> >> >
> >> > I don't follow? Won't it cause a regression?
> >>
> >> Not at all. We use the "individual care" pattern upstream now,
> >> specifically for those MSRs (kvmclock) for which the qemu-kvm code was
> >> introduced.
> >
> > I mean a future regression with current+patch qemu and a new kernel.
>
> For sane scenarios, such a combination should never expose new (ie.
> unknown from qemu's POV) MSRs to the guest. Thus not clearing them
> cannot cause any harm.
The problem is with hardware MSRs (PV MSRs are protected by cpuid, and
always disable themselves when zeroed).
> BTW, you also do not know if 0 will be the right reset value for these
> to-be-invented MSRs. That could cause regression as well.
What I suggested wasn't zeroing them, but writing the value we read just
after vcpu creation.
We had a regression when we started supporting PAT. Zeroing it causes
the cache to be disabled, making everything ridiculously slow. We now
special case it; my proposed solution would have taken care of it.
--
error compiling committee.c: too many arguments to function
next prev parent reply other threads:[~2011-05-05 10:28 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-04 19:43 [PATCH 00/19] qemu-kvm: Cleanup and switch to upstream - Part I Jan Kiszka
2011-05-04 19:43 ` [PATCH 01/19] qemu-kvm: Switch to upstream mp_state functions Jan Kiszka
2011-05-04 19:43 ` [PATCH 02/19] qemu-kvm: x86: Use upstream kvmclock device Jan Kiszka
2011-05-04 19:43 ` [PATCH 03/19] Revert "introduce VMSTATE_U64" Jan Kiszka
2011-05-04 19:43 ` [PATCH 04/19] qemu-kvm: x86: Drop MSR reset Jan Kiszka
2011-05-05 8:08 ` Avi Kivity
2011-05-05 8:11 ` Jan Kiszka
2011-05-05 8:16 ` Avi Kivity
2011-05-05 8:27 ` Jan Kiszka
2011-05-05 8:33 ` Avi Kivity
2011-05-05 8:44 ` Jan Kiszka
2011-05-05 8:53 ` Avi Kivity
2011-05-05 9:32 ` Jan Kiszka
2011-05-05 10:22 ` Avi Kivity [this message]
2011-05-05 10:36 ` Jan Kiszka
2011-05-05 11:57 ` Avi Kivity
2011-05-05 11:22 ` Gleb Natapov
2011-05-05 11:58 ` Avi Kivity
2011-05-05 12:23 ` Gleb Natapov
2011-05-05 12:42 ` Jan Kiszka
2011-05-05 13:33 ` Marcelo Tosatti
2011-05-05 18:08 ` Gleb Natapov
2011-05-04 19:43 ` [PATCH 05/19] qemu-kvm: Use upstream VCPU reset services Jan Kiszka
2011-05-04 19:43 ` [PATCH 06/19] qemu-kvm: Use upstream vcpu initialization Jan Kiszka
2011-05-04 19:43 ` [PATCH 07/19] qemu-kvm: Start using qemu-thread services Jan Kiszka
2011-05-04 19:43 ` [PATCH 08/19] qemu-kvm: Use upstream kvm_arch_get/put_registers Jan Kiszka
2011-05-04 19:43 ` [PATCH 09/19] qemu-kvm: Use upstream state synchronization services Jan Kiszka
2011-05-04 19:43 ` [PATCH 10/19] qemu-kvm: Drop remaining libkvm fragments Jan Kiszka
2011-05-04 19:43 ` [PATCH 11/19] qemu-kvm: Drop some more unused code Jan Kiszka
2011-05-04 19:43 ` [PATCH 12/19] qemu-kvm: Drop some obsolete/unused fields from kvm_context Jan Kiszka
2011-05-04 19:43 ` [PATCH 13/19] qemu-kvm: Refactor in-kernel irqchip and pit control Jan Kiszka
2011-05-04 19:43 ` [PATCH 14/19] qemu-kvm: Fold kvm_create into kvm_create_context Jan Kiszka
2011-05-04 19:43 ` [PATCH 15/19] qemu-kvm: Fold kvm_arch_qemu_create_context into kvm_arch_create Jan Kiszka
2011-05-04 19:43 ` [PATCH 16/19] qemu-kvm: Push PIT reinjection control into x86 code Jan Kiszka
2011-05-04 19:43 ` [PATCH 17/19] qemu-kvm: Replace kvm_show_regs/code with cpu_dump_state Jan Kiszka
2011-05-04 19:43 ` [PATCH 18/19] qemu-kvm: Fold kvm_init_coalesced_mmio into kvm_create_context Jan Kiszka
2011-05-04 19:43 ` [PATCH 19/19] qemu-kvm: x86: Use kvm_arch_init Jan Kiszka
2011-05-05 8:22 ` [PATCH 00/19] qemu-kvm: Cleanup and switch to upstream - Part I Avi Kivity
2011-05-05 8:29 ` Jan Kiszka
2011-05-06 13:51 ` Marcelo Tosatti
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