From: Kevin O'Connor <kevin@koconnor.net>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Xu, Anthony" <anthony.xu@intel.com>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>
Subject: Re: [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode
Date: Fri, 12 May 2017 15:38:40 -0400 [thread overview]
Message-ID: <20170512193840.GA22454@morn.lan> (raw)
In-Reply-To: <f9c33614-be36-e789-b72b-b4ffcc8bb6a8@redhat.com>
On Fri, May 12, 2017 at 09:16:31PM +0200, Paolo Bonzini wrote:
> On 12/05/2017 20:55, Xu, Anthony wrote:
> > If that's the case, QEMU/TCG should work with SeaBios even with ignoring A20.
> >
> > During SeaBios boot, there are >350 port 92 access, if we don't need to handle A20,
> > we can make A20 configurable in Seabios, It may reduce SeaBios boot time.
>
> Yes, that's a good idea.
SeaBIOS defaults to enabling A20 and it's a rare beast that disables
it. One could change x86.h:set_a20 and romlayout.S:transition32 to
only issue the outb() if the inb() indicates a change is needed. That
would likely eliminate half the accesses.
I'd be surprised if it would impact the overall boot time though.
SeaBIOS only touches the port on a cpu mode switch and I would have
thought that was heavier than an IO port access. Maybe that is skewed
on KVM though.
-Kevin
next prev parent reply other threads:[~2017-05-12 19:38 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-11 11:35 [Qemu-devel] [PATCH] target/i386: enable A20 automatically in system management mode Paolo Bonzini
2017-05-11 11:41 ` no-reply
2017-05-11 11:58 ` no-reply
2017-05-11 14:53 ` Kevin O'Connor
2017-05-11 15:32 ` Paolo Bonzini
2017-05-11 16:34 ` Kevin O'Connor
2017-05-11 23:55 ` Xu, Anthony
2017-05-12 12:16 ` Paolo Bonzini
2017-05-12 18:55 ` Xu, Anthony
2017-05-12 19:16 ` Paolo Bonzini
2017-05-12 19:38 ` Kevin O'Connor [this message]
2017-05-12 23:19 ` Xu, Anthony
2017-05-13 0:01 ` Kevin O'Connor
2017-05-13 1:24 ` Xu, Anthony
2017-05-16 16:24 ` Kevin O'Connor
2017-05-16 20:00 ` Xu, Anthony
2017-05-16 21:42 ` Kevin O'Connor
2017-05-16 22:39 ` Xu, Anthony
2017-05-17 8:18 ` Paolo Bonzini
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