From: Ingo Molnar <mingo@elte.hu>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Yinghai Lu <yinghai@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org,
Suresh Siddha <suresh.b.siddha@intel.com>
Subject: Re: [PATCH] x86: Don't write io_apic ID if it is not changed
Date: Mon, 16 Aug 2010 09:28:05 +0200 [thread overview]
Message-ID: <20100816072805.GA22479@elte.hu> (raw)
In-Reply-To: <m1hbiv6fcb.fsf@fess.ebiederm.org>
* Eric W. Biederman <ebiederm@xmission.com> wrote:
> Yinghai Lu <yinghai@kernel.org> writes:
>
> > For 32bit mptable path, setup_ids_from_mpc() always write io apic id
> > register, even there is no change needed.
> >
> > So try to do that when they are different bewteen reading out and
> > mptable
>
> What is the advantage of not writing the value?
Just guessing, but if other OSs dont do it we might surprise buggy hardware
[and trigger erratas in them], so this would be a standard 'dont touch the hw
unless necessary' defensive move.
Similar bugs are not unprecedented.
Thanks,
Ingo
prev parent reply other threads:[~2010-08-16 7:28 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-14 20:38 [PATCH] x86: Don't write io_apic ID if it is not changed Yinghai Lu
2010-08-15 8:24 ` Cyrill Gorcunov
2010-08-15 8:30 ` Cyrill Gorcunov
2010-08-16 9:06 ` Cyrill Gorcunov
2010-08-15 15:55 ` Eric W. Biederman
2010-08-16 7:28 ` Ingo Molnar [this message]
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