From: "H. Peter Anvin" <hpa@zytor.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
kvm@vger.kernel.org, Avi Kivity <avi@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
Ingo Molnar <mingo@redhat.com>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] kvm: optimize ISR lookups
Date: Mon, 21 May 2012 16:12:21 -0700 [thread overview]
Message-ID: <4FBACBD5.6080207@zytor.com> (raw)
In-Reply-To: <20120521230623.GO17031@redhat.com>
On 05/21/2012 04:06 PM, Michael S. Tsirkin wrote:
>
> I think the reason is __apic_read which now simply copies the registers
> out to guest, this code will become less straight-forward if it's not
> 1:1.
>
It can still be 1:1, just drop the 12 bytes of completely useless
padding after each 32-bit datum.
>> And if you look deeper, then you'll notice that _ALL_ APIC registers
>> are on a 16 byte boundary (thanks Peter for pointing that out).
>>
>> So it's even more silly to have a 1:1 representation instead of
>> implementing the default emulated apic_read/write functions to access
>> (offset >> 2).
>>
>> And of course, that design decision causes lookups to be slow.
>
> Yes, it might be one of the reasons why my patch helps so
> much: it adds a cache in front of this data structure.
>
Well, *fix the fscking data structure first*.
>
> So what you propose is in fact to rework apic registers at least for
> ISR,IRR,TMR to use a bitmap.
> I am fine with this suggestion but would like some feedback from kvm
> maintainers on where they want to go before I spend time on that.
>
This should be a 20-minute hack.
-hpa
next prev parent reply other threads:[~2012-05-21 23:12 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-21 16:37 [PATCH] kvm: optimize ISR lookups Michael S. Tsirkin
2012-05-21 18:44 ` Michael S. Tsirkin
2012-05-21 21:04 ` Thomas Gleixner
2012-05-21 21:51 ` Michael S. Tsirkin
2012-05-21 22:14 ` Thomas Gleixner
2012-05-21 22:24 ` Michael S. Tsirkin
2012-05-21 22:44 ` Thomas Gleixner
2012-05-21 22:50 ` Michael S. Tsirkin
2012-05-21 23:01 ` Thomas Gleixner
2012-05-22 10:46 ` Avi Kivity
2012-05-23 14:48 ` Ingo Molnar
2012-05-23 15:03 ` Avi Kivity
2012-05-23 20:10 ` Thomas Gleixner
2012-05-23 20:46 ` Michael S. Tsirkin
2012-05-23 23:02 ` Thomas Gleixner
2012-05-23 15:14 ` Michael S. Tsirkin
2012-05-23 19:22 ` H. Peter Anvin
2012-05-21 23:11 ` Thomas Gleixner
2012-05-21 23:06 ` Michael S. Tsirkin
2012-05-21 23:12 ` H. Peter Anvin [this message]
2012-05-21 23:36 ` Thomas Gleixner
2012-05-22 10:59 ` Avi Kivity
2012-05-22 17:26 ` Thomas Gleixner
2012-05-23 15:10 ` Avi Kivity
2012-05-23 18:37 ` Thomas Gleixner
2012-05-23 19:25 ` H. Peter Anvin
2012-05-23 22:00 ` Thomas Gleixner
2012-05-30 14:18 ` Avi Kivity
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