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In many cases, especially in networking, it can be beneficial to know at compile time whether the architecture can do unaligned accesses efficiently. This patch introduces a new Kconfig symbol HAVE_EFFICIENT_UNALIGNED_ACCESS for that purpose and adds it to the powerpc and x86 architectures. Also add some documentation about alignment and networking, and especially one intended use of this symbol. Signed-off-by: Johannes Berg <johannes@sipsolutions.net> Acked-by: Sam Ravnborg <sam@ravnborg.org> Acked-by: Ingo Molnar <mingo@elte.hu> [x86 architecture part] Cc: <linux-arch@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
73 lines
1.9 KiB
Text
73 lines
1.9 KiB
Text
#
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# General architecture dependent options
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#
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config OPROFILE
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tristate "OProfile system profiling (EXPERIMENTAL)"
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depends on PROFILING
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depends on HAVE_OPROFILE
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help
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OProfile is a profiling system capable of profiling the
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whole system, include the kernel, kernel modules, libraries,
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and applications.
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If unsure, say N.
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config HAVE_OPROFILE
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def_bool n
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config KPROBES
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bool "Kprobes"
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depends on KALLSYMS && MODULES
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depends on HAVE_KPROBES
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help
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Kprobes allows you to trap at almost any kernel address and
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execute a callback function. register_kprobe() establishes
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a probepoint and specifies the callback. Kprobes is useful
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for kernel debugging, non-intrusive instrumentation and testing.
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If in doubt, say "N".
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config HAVE_EFFICIENT_UNALIGNED_ACCESS
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def_bool n
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help
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Some architectures are unable to perform unaligned accesses
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without the use of get_unaligned/put_unaligned. Others are
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unable to perform such accesses efficiently (e.g. trap on
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unaligned access and require fixing it up in the exception
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handler.)
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This symbol should be selected by an architecture if it can
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perform unaligned accesses efficiently to allow different
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code paths to be selected for these cases. Some network
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drivers, for example, could opt to not fix up alignment
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problems with received packets if doing so would not help
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much.
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See Documentation/unaligned-memory-access.txt for more
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information on the topic of unaligned memory accesses.
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config KRETPROBES
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def_bool y
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depends on KPROBES && HAVE_KRETPROBES
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config HAVE_IOREMAP_PROT
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def_bool n
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config HAVE_KPROBES
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def_bool n
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config HAVE_KRETPROBES
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def_bool n
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config HAVE_DMA_ATTRS
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def_bool n
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config USE_GENERIC_SMP_HELPERS
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def_bool n
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config HAVE_CLK
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def_bool n
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help
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The <linux/clk.h> calls support software clock gating and
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thus are a key power management tool on many systems.
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