From: Keir Fraser <keir.fraser@eu.citrix.com>
To: Kouya Shimura <kouya@jp.fujitsu.com>
Cc: "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>
Subject: Re: [PATCH] x86 hvm: freeze PIT/LAPIC timer emulation while its IRQ is masked
Date: Thu, 10 Sep 2009 13:32:32 +0100 [thread overview]
Message-ID: <C6CEB070.145C7%keir.fraser@eu.citrix.com> (raw)
In-Reply-To: <7kd45z6s6z.fsf@pingu.sky.yk.fujitsu.co.jp>
On 10/09/2009 10:54, "Kouya Shimura" <kouya@jp.fujitsu.com> wrote:
>> Not using pt_irq_masked() seems odd. Is it to avoid 859 IRQ mask checks, and
>> if so why are you doing that? Why do we care that rombios twiddles the 8259
>> masks a bunch during boot?
>
> I guessed that the cost of freezing/thawing a timer with the 8259 mask
> is higher than timer emulation. And the PIT timer is actually active
> while rombios masks the 8259.
>
> If using pt_irq_masked() is desirable, I'll remake it.
If your patch works without even any theoretical lost of correctness, then
that makes it more attractive, obviously.
Some evidence that the cost saving is at all measurable would also be good.
Premature optimisation being evil, etc. ;-)
-- Keir
next prev parent reply other threads:[~2009-09-10 12:32 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-09-10 5:47 [PATCH] x86 hvm: freeze PIT/LAPIC timer emulation while its IRQ is masked Kouya Shimura
2009-09-10 6:49 ` Keir Fraser
2009-09-10 8:22 ` Kouya Shimura
2009-09-10 8:32 ` Keir Fraser
2009-09-10 9:54 ` Kouya Shimura
2009-09-10 12:32 ` Keir Fraser [this message]
2009-09-16 6:46 ` Kouya Shimura
2009-09-16 6:50 ` [PATCH 1/2] x86 hvm: don't set periodical timer again until its IRQ is delivered Kouya Shimura
2009-09-16 6:53 ` [PATCH 2/2] x86 hvm: suspend platform timer emulation while its IRQ is masked Kouya Shimura
2009-09-16 7:40 ` [PATCH] x86 hvm: freeze PIT/LAPIC " Keir Fraser
2009-09-16 8:00 ` Cui, Dexuan
2009-09-16 8:20 ` Keir Fraser
2009-09-16 8:40 ` Cui, Dexuan
2009-09-16 9:09 ` Keir Fraser
2009-09-16 8:28 ` Kouya Shimura
2009-09-16 8:36 ` Keir Fraser
2009-09-11 12:07 ` Konrad Rzeszutek Wilk
2009-09-14 5:58 ` Kouya Shimura
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