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Baoquan He bee3204ec3 x86/apic: Set up through-local-APIC mode on the boot CPU if 'noapic' specified 
Currently the kdump kernel becomes very slow if 'noapic' is specified.
Normal kernel doesn't have this bug.

Kernel parameter 'noapic' is used to disable IO-APIC in system for
testing or special purpose. Here the root cause is that in kdump
kernel LAPIC is disabled since commit:

  522e664644 ("x86/apic: Disable I/O APIC before shutdown of the local APIC")

In this case we need set up through-local-APIC on boot CPU in
setup_local_APIC().

In normal kernel the legacy irq mode is enabled by the BIOS. If
it is virtual wire mode, the local-APIC has been enabled and set as
through-local-APIC.

Though we fixed the regression introduced by commit 522e664644,
to further improve robustness set up the through-local-APIC mode
explicitly, do not rely on the default boot IRQ mode.

Signed-off-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Eric W. Biederman <ebiederm@xmission.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: douly.fnst@cn.fujitsu.com
Cc: joro@8bytes.org
Cc: prarit@redhat.com
Cc: uobergfe@redhat.com
Link: http://lkml.kernel.org/r/20180214054656.3780-7-bhe@redhat.com
[ Rewrote the changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-02-17 11:47:46 +01:00
arch x86/apic: Set up through-local-APIC mode on the boot CPU if 'noapic' specified 2018-02-17 11:47:46 +01:00
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README 

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.