From: Ingo Molnar <mingo@kernel.org>
To: Yinghai Lu <yinghai@kernel.org>
Cc: "Wang, Song-Bo (Stoney)" <song-bo.wang@hp.com>,
"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@elte.hu>,
Thomas Gleixner <tglx@linutronix.de>,
"Zhang, Lin-Bao (Linux Kernel R&D)" <linbao.zhang@hp.com>,
"Pearson, Greg" <greg.pearson@hp.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"suresh.b.siddha@intel.com" <suresh.b.siddha@intel.com>
Subject: Re: [PATCH] x86/apic: check FADT settings after enable x2apic
Date: Tue, 29 Jan 2013 08:47:46 +0100 [thread overview]
Message-ID: <20130129074746.GA594@gmail.com> (raw)
In-Reply-To: <CAE9FiQUtQ4uaBZxndV+acHW55JL5-nb0EnuXHhwiB-mK8Swtag@mail.gmail.com>
* Yinghai Lu <yinghai@kernel.org> wrote:
> On Mon, Jan 28, 2013 at 2:11 AM, Ingo Molnar <mingo@kernel.org> wrote:
> >
> >> HP has systems that work with x2apic phys mode and BIOS set
> >> ACPI_FADT_APIC_PHYSICAL in FADT table, and all cpuid < 255,
> >> the spec requires BIOS only put system on xapic mode. Kernel
> >
> > Which spec?
> >
> >> will set to x2apic logical mode instead of x2apic phys mode.
> >
> > Which has exactly what bad effect on users of these systems?
> >
> > You left out the most important information from the changelog:
> > why do users care, what good does the patch do?
>
> please check you are happy with this:
>
> ---
> From: Stoney Wang <song-bo.wang@hp.com>
> Subject: [PATCH] x86, apic: Check fadt x2apic phys in x2apic_phys_probe()
>
> HP has systems that only work with x2apic phys mode and BIOS set
> ACPI_FADT_APIC_PHYSICAL in FADT table. But all apicid < 255,
> according to x2apic-spec, chapter 2.9, BIOS need to pass the control
> to the OS with xapic mode.
> Kernel will set apic driver wrong to x2apic cluster instead of x2apic phys.
>
> The user will have to append nox2apic in boot command line to stay xapic mode,
> or append x2apic_phys to switch to x2apic phys mode.
This still does not explain what happens if none of this user
action is taken. I.e. what exact _user visible problem_ does the
patch fix?
Is this really so unimportant to you? Almost everyone will start
a changelog with explaining what badness happens. Not you - you
explain everything from how the fix works to how to work around
the bug - except describing the most important thing: theuser
visible problem itself ... Weird.
Thanks,
Ingo
next prev parent reply other threads:[~2013-01-29 7:47 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-15 1:50 [PATCH] x86/apic: check FADT settings after enable x2apic Stoney Wang
2013-01-28 5:05 ` Wang, Song-Bo (Stoney)
2013-01-28 6:57 ` Yinghai Lu
2013-01-28 10:11 ` Ingo Molnar
2013-01-28 18:10 ` Yinghai Lu
2013-01-29 7:47 ` Ingo Molnar [this message]
2013-01-29 8:43 ` Wang, Song-Bo (Stoney)
2013-01-29 8:49 ` Ingo Molnar
2013-01-29 21:30 ` Yinghai Lu
2013-01-29 21:52 ` Yinghai Lu
2013-01-31 11:32 ` Ingo Molnar
2013-01-31 15:56 ` Yinghai Lu
2013-02-04 6:41 ` Wang, Song-Bo (Stoney)
2013-02-04 11:03 ` Ingo Molnar
2013-02-04 20:29 ` [PATCH] x86, apic: Check fadt x2apic phys in x2apic_phys_probe() Yinghai Lu
2013-02-05 12:24 ` Ingo Molnar
2013-02-05 16:53 ` Yinghai Lu
2013-02-06 13:16 ` Ingo Molnar
2013-02-06 17:10 ` Yinghai Lu
2013-02-07 18:53 ` [PATCH v4] " Yinghai Lu
2013-02-11 12:37 ` [tip:x86/urgent] x86/apic: Work around boot failure on HP ProLiant DL980 G7 Server systems tip-bot for Stoney Wang
2013-02-18 8:52 ` [PATCH v4] x86, apic: Check fadt x2apic phys in x2apic_phys_probe() Lin-Bao Zhang
2013-02-18 17:13 ` Yinghai Lu
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