From: cdall@cs.columbia.edu (Christoffer Dall)
To: linux-arm-kernel@lists.infradead.org
Subject: [kvmarm] [PATCH 09/29] arm64: KVM: system register handling
Date: Tue, 23 Apr 2013 16:07:05 -0700 [thread overview]
Message-ID: <CAEDV+gKjL=XDBXpC+Dh18yf7MwKhKiAVWZiU_1tgaLUJQkV-vg@mail.gmail.com> (raw)
In-Reply-To: <40f45d8ddae65e29a6145bbe5c96d0bb@localhost>
On Mon, Mar 25, 2013 at 1:19 AM, Marc Zyngier <marc.zyngier@arm.com> wrote:
> Hi Alex,
>
> On Thu, 7 Mar 2013 11:30:20 +0100, Alexander Graf <agraf@suse.de> wrote:
>> On 05.03.2013, at 04:47, Marc Zyngier wrote:
>>
>>> Provide 64bit system register handling, modeled after the cp15
>>> handling for ARM.
>>>
>>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>>> ---
>
> [...]
>
>>> +static int emulate_sys_reg(struct kvm_vcpu *vcpu,
>>> + const struct sys_reg_params *params)
>>> +{
>>> + size_t num;
>>> + const struct sys_reg_desc *table, *r;
>>> +
>>> + table = get_target_table(vcpu->arch.target, &num);
>>> +
>>> + /* Search target-specific then generic table. */
>>> + r = find_reg(params, table, num);
>>> + if (!r)
>>> + r = find_reg(params, sys_reg_descs, ARRAY_SIZE(sys_reg_descs));
>>
>> Searching through the whole list sounds quite slow. Especially since the
>> TLS register is at the very bottom of it.
>>
>> Can't you make this a simple switch() statement through a bit of #define
>> and maybe #include magic? After all, the sysreg target encoding is all
> part
>> of the opcode. And from my experience in the PPC instruction emulator,
>> switch()es are _a lot_ faster than any other way of lookup I've tried.
>
> So I've had a go at implementing this, and decided it is not worth the
> effort if we want to preserve the same level of functionality (ONE_REG
> discovery, sanity checking at VM startup...).
>
> Granted, we would gain a faster trap handling. But look at what we're
> actually trapping, and how often this happens. Almost nothing, almost
> never. So, until shown that we spend too much time iterating over the
> sys_reg_desc array, I'll keep it simple.
>
> This is not to say that there's no optimization to be made. Quite the
> opposite! Just that this particular one seems a bit overkill.
>
> Anyway, thanks for pushing me into pondering this! :-)
>
totally late in the game here, but I saw you discussed this briefly on
IRC as well, and I completely agree with Marc here, we have much
bigger fish to fry. On all the measurements I did on the 32-bit side,
this doesn't even begin to show up on the radar.
vgic man, vgic!
-Christoffer
next prev parent reply other threads:[~2013-04-23 23:07 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-05 3:47 [PATCH 00/29] Port of KVM to arm64 Marc Zyngier
2013-03-05 3:47 ` [PATCH 01/29] arm64: KVM: define HYP and Stage-2 translation page flags Marc Zyngier
2013-03-05 3:47 ` [PATCH 02/29] arm64: KVM: HYP mode idmap support Marc Zyngier
2013-03-05 3:47 ` [PATCH 03/29] arm64: KVM: EL2 register definitions Marc Zyngier
2013-03-05 3:47 ` [PATCH 04/29] arm64: KVM: system register definitions for 64bit guests Marc Zyngier
2013-03-07 10:33 ` [kvmarm] " Alexander Graf
2013-03-08 3:23 ` Marc Zyngier
2013-03-12 13:20 ` Christopher Covington
2013-03-12 13:41 ` Christopher Covington
2013-03-12 13:50 ` Marc Zyngier
2013-03-05 3:47 ` [PATCH 05/29] arm64: KVM: Basic ESR_EL2 helpers and vcpu register access Marc Zyngier
2013-03-16 0:55 ` Geoff Levand
2013-03-05 3:47 ` [PATCH 06/29] arm64: KVM: fault injection into a guest Marc Zyngier
2013-03-12 13:20 ` Christopher Covington
2013-03-12 14:25 ` Marc Zyngier
2013-03-16 1:03 ` Geoff Levand
2013-03-05 3:47 ` [PATCH 07/29] arm64: KVM: architecture specific MMU backend Marc Zyngier
2013-03-05 3:47 ` [PATCH 08/29] arm64: KVM: user space interface Marc Zyngier
2013-03-07 8:09 ` Michael S. Tsirkin
2013-03-08 3:46 ` [kvmarm] " Marc Zyngier
2013-03-10 9:23 ` Michael S. Tsirkin
2013-03-05 3:47 ` [PATCH 09/29] arm64: KVM: system register handling Marc Zyngier
2013-03-07 10:30 ` [kvmarm] " Alexander Graf
2013-03-08 3:29 ` Marc Zyngier
2013-03-25 8:19 ` Marc Zyngier
2013-04-23 23:07 ` Christoffer Dall [this message]
2013-03-05 3:47 ` [PATCH 10/29] arm64: KVM: Cortex-A57 specific system registers handling Marc Zyngier
2013-03-13 18:30 ` Christopher Covington
2013-03-14 10:26 ` Marc Zyngier
2013-03-05 3:47 ` [PATCH 11/29] arm64: KVM: virtual CPU reset Marc Zyngier
2013-03-05 3:47 ` [PATCH 12/29] arm64: KVM: kvm_arch and kvm_vcpu_arch definitions Marc Zyngier
2013-03-12 17:30 ` Christopher Covington
2013-03-05 3:47 ` [PATCH 13/29] arm64: KVM: MMIO access backend Marc Zyngier
2013-03-05 3:47 ` [PATCH 14/29] arm64: KVM: guest one-reg interface Marc Zyngier
2013-03-12 17:31 ` Christopher Covington
2013-03-12 18:05 ` Marc Zyngier
2013-03-12 22:07 ` Christopher Covington
2013-03-13 7:48 ` Marc Zyngier
2013-03-13 20:34 ` Christopher Covington
2013-03-14 8:57 ` [kvmarm] " Peter Maydell
2013-03-20 20:06 ` Christopher Covington
2013-03-05 3:47 ` [PATCH 15/29] arm64: KVM: hypervisor initialization code Marc Zyngier
2013-03-05 3:47 ` [PATCH 16/29] arm64: KVM: HYP mode world switch implementation Marc Zyngier
2013-03-13 19:59 ` Christopher Covington
2013-03-20 20:04 ` Christopher Covington
2013-03-21 11:54 ` Marc Zyngier
2013-03-05 3:47 ` [PATCH 17/29] arm64: KVM: Exit handling Marc Zyngier
2013-03-05 3:47 ` [PATCH 18/29] arm64: KVM: Plug the VGIC Marc Zyngier
2013-03-05 3:47 ` [PATCH 19/29] arm64: KVM: Plug the arch timer Marc Zyngier
2013-03-05 3:47 ` [PATCH 20/29] arm64: KVM: PSCI implementation Marc Zyngier
2013-03-05 3:47 ` [PATCH 21/29] arm64: KVM: Build system integration Marc Zyngier
2013-03-05 3:47 ` [PATCH 22/29] arm64: KVM: define 32bit specific registers Marc Zyngier
2013-03-18 17:03 ` Christopher Covington
2013-03-05 3:47 ` [PATCH 23/29] arm64: KVM: 32bit GP register access Marc Zyngier
2013-03-16 0:24 ` Geoff Levand
2013-03-05 3:47 ` [PATCH 24/29] arm64: KVM: 32bit conditional execution emulation Marc Zyngier
2013-03-18 17:04 ` Christopher Covington
2013-03-05 3:47 ` [PATCH 25/29] arm64: KVM: 32bit handling of coprocessor traps Marc Zyngier
2013-03-05 3:47 ` [PATCH 26/29] arm64: KVM: 32bit coprocessor access for Cortex-A57 Marc Zyngier
2013-03-05 3:47 ` [PATCH 27/29] arm64: KVM: 32bit specific register world switch Marc Zyngier
2013-03-05 3:47 ` [PATCH 28/29] arm64: KVM: 32bit guest fault injection Marc Zyngier
2013-03-18 18:45 ` Christopher Covington
2013-03-05 3:47 ` [PATCH 29/29] arm64: KVM: enable initialization of a 32bit vcpu Marc Zyngier
2013-03-18 18:56 ` Christopher Covington
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