linux/include/asm-generic/percpu.h, branch v3.16

percpu: add raw_cpu_ops

2014-04-07T23:36:13Z

The kernel has never been audited to ensure that this_cpu operations are consistently used throughout the kernel. The code generated in many places can be improved through the use of this_cpu operations (which uses a segment register for relocation of per cpu offsets instead of performing address calculations). The patch set also addresses various consistency issues in general with the per cpu macros. A. The semantics of __this_cpu_ptr() differs from this_cpu_ptr only because checks are skipped. This is typically shown through a raw_ prefix. So this patch set changes the places where __this_cpu_ptr() is used to raw_cpu_ptr(). B. There has been the long term wish by some that __this_cpu operations would check for preemption. However, there are cases where preemption checks need to be skipped. This patch set adds raw_cpu operations that do not check for preemption and then adds preemption checks to the __this_cpu operations. C. The use of __get_cpu_var is always a reference to a percpu variable that can also be handled via a this_cpu operation. This patch set replaces all uses of __get_cpu_var with this_cpu operations. D. We can then use this_cpu RMW operations in various places replacing sequences of instructions by a single one. E. The use of this_cpu operations throughout will allow other arches than x86 to implement optimized references and RMV operations to work with per cpu local data. F. The use of this_cpu operations opens up the possibility to further optimize code that relies on synchronization through per cpu data. The patch set works in a couple of stages: I. Patch 1 adds the additional raw_cpu operations and raw_cpu_ptr(). Also converts the existing __this_cpu_xx_# primitive in the x86 code to raw_cpu_xx_#. II. Patch 2-4 use the raw_cpu operations in places that would give us false positives once they are enabled. III. Patch 5 adds preemption checks to __this_cpu operations to allow checking if preemption is properly disabled when these functions are used. IV. Patches 6-20 are patches that simply replace uses of __get_cpu_var with this_cpu_ptr. They do not depend on any changes to the percpu code. No preemption tests are skipped if they are applied. V. Patches 21-46 are conversion patches that use this_cpu operations in various kernel subsystems/drivers or arch code. VI. Patches 47/48 (not included in this series) remove no longer used functions (__this_cpu_ptr and __get_cpu_var). These should only be applied after all the conversion patches have made it and after we have done additional passes through the kernel to ensure that none of the uses of these functions remain. This patch (of 46): The patches following this one will add preemption checks to __this_cpu ops so we need to have an alternative way to use this_cpu operations without preemption checks. raw_cpu_ops will be the basis for all other ops since these will be the operations that do not implement any checks. Primitive operations are renamed by this patch from __this_cpu_xxx to raw_cpu_xxxx. Also change the uses of the x86 percpu primitives in preempt.h. These depend directly on asm/percpu.h (header #include nesting issue). Signed-off-by: Peter Zijlstra Signed-off-by: Christoph Lameter Acked-by: Ingo Molnar Cc: Tejun Heo Cc: "James E.J. Bottomley" Cc: "Paul E. McKenney" Cc: Alex Shi Cc: Arnd Bergmann Cc: Benjamin Herrenschmidt Cc: Bryan Wu Cc: Catalin Marinas Cc: Chris Metcalf Cc: Daniel Lezcano Cc: David Daney Cc: David Miller Cc: David S. Miller Cc: Dimitri Sivanich Cc: Dipankar Sarma Cc: Eric Dumazet Cc: Fenghua Yu Cc: Frederic Weisbecker Cc: Greg Kroah-Hartman Cc: H. Peter Anvin Cc: Haavard Skinnemoen Cc: Hans-Christian Egtvedt Cc: Hedi Berriche Cc: Heiko Carstens Cc: Helge Deller Cc: Ivan Kokshaysky Cc: James Hogan Cc: Jens Axboe Cc: John Stultz Cc: Martin Schwidefsky Cc: Masami Hiramatsu Cc: Matt Turner Cc: Mike Frysinger Cc: Mike Travis Cc: Neil Brown Cc: Nicolas Pitre Cc: Paul Mackerras Cc: Paul Mundt Cc: Rafael J. Wysocki Cc: Ralf Baechle Cc: Richard Henderson Cc: Robert Richter Cc: Russell King Cc: Russell King Cc: Rusty Russell Cc: Steven Rostedt Cc: Thomas Gleixner Cc: Tony Luck Cc: Will Deacon Cc: Wim Van Sebroeck Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

percpu: Optimize __get_cpu_var()

2010-09-10T08:56:51Z

Redefine __get_cpu_var() using this_cpu_ptr() which can be arch-optimized. Signed-off-by: Brian Gerst Signed-off-by: Tejun Heo

x86, percpu: Optimize this_cpu_ptr

2010-09-10T08:56:47Z

Allow arches to implement __this_cpu_ptr, and provide an x86 version. Before: movq $foo, %rax movq %gs:this_cpu_off, %rdx addq %rdx, %rax After: movq $foo, %rax addq %gs:this_cpu_off, %rax The benefit is doing it in one less instruction and not clobbering a temporary register. tj: * Beefed up the comment a bit and renamed in-macro temp variable to match neighboring macros. * Folded fix for const pointer case found in linux-next. * Fixed sparse notation. Signed-off-by: Brian Gerst Signed-off-by: Tejun Heo

percpu: handle __percpu notations in UP accessors

2010-08-07T12:20:53Z

UP accessors didn't take care of __percpu notations leading to a lot of spurious sparse warnings on UP configurations. Fix it. Signed-off-by: Namhyung Kim Signed-off-by: Tejun Heo

Merge branch 'for-35' of git://repo.or.cz/linux-kbuild

2010-06-01T15:55:52Z

* 'for-35' of git://repo.or.cz/linux-kbuild: (81 commits) kbuild: Revert part of e8d400a to resolve a conflict kbuild: Fix checking of scm-identifier variable gconfig: add support to show hidden options that have prompts menuconfig: add support to show hidden options which have prompts gconfig: remove show_debug option gconfig: remove dbg_print_ptype() and dbg_print_stype() kconfig: fix zconfdump() kconfig: some small fixes add random binaries to .gitignore kbuild: Include gen_initramfs_list.sh and the file list in the .d file kconfig: recalc symbol value before showing search results .gitignore: ignore *.lzo files headerdep: perlcritic warning scripts/Makefile.lib: Align the output of LZO kbuild: Generate modules.builtin in make modules_install Revert "kbuild: specify absolute paths for cscope" kbuild: Do not unnecessarily regenerate modules.builtin headers_install: use local file handles headers_check: fix perl warnings export_report: fix perl warnings ...

Rename .data[.percpu][.XXX] to .data[..percpu][..XXX].

2010-03-03T10:26:00Z

Signed-off-by: Denys Vlasenko Signed-off-by: Michal Marek

percpu: make accessors check for percpu pointer in sparse

2009-10-29T13:34:15Z

The previous patch made sparse warn about percpu variables being used directly without going through percpu accessors. This patch implements the other half - checking whether non percpu variable is passed into percpu accessors. Signed-off-by: Tejun Heo Cc: Rusty Russell Cc: Al Viro

percpu: add __percpu for sparse.

2009-10-29T13:34:15Z

We have to make __kernel "__attribute__((address_space(0)))" so we can cast to it. tj: * put_cpu_var() update. * Annotations added to dynamic allocator interface. Signed-off-by: Rusty Russell Cc: Al Viro Signed-off-by: Tejun Heo

percpu: remove per_cpu__ prefix.

2009-10-29T13:34:15Z

Now that the return from alloc_percpu is compatible with the address of per-cpu vars, it makes sense to hand around the address of per-cpu variables. To make this sane, we remove the per_cpu__ prefix we used created to stop people accidentally using these vars directly. Now we have sparse, we can use that (next patch). tj: * Updated to convert stuff which were missed by or added after the original patch. * Kill per_cpu_var() macro. Signed-off-by: Rusty Russell Signed-off-by: Tejun Heo Reviewed-by: Christoph Lameter

this_cpu: Introduce this_cpu_ptr() and generic this_cpu_* operations

2009-10-03T10:48:22Z

This patch introduces two things: First this_cpu_ptr and then per cpu atomic operations. this_cpu_ptr ------------ A common operation when dealing with cpu data is to get the instance of the cpu data associated with the currently executing processor. This can be optimized by this_cpu_ptr(xx) = per_cpu_ptr(xx, smp_processor_id). The problem with per_cpu_ptr(x, smp_processor_id) is that it requires an array lookup to find the offset for the cpu. Processors typically have the offset for the current cpu area in some kind of (arch dependent) efficiently accessible register or memory location. We can use that instead of doing the array lookup to speed up the determination of the address of the percpu variable. This is particularly significant because these lookups occur in performance critical paths of the core kernel. this_cpu_ptr() can avoid memory accesses and this_cpu_ptr comes in two flavors. The preemption context matters since we are referring the the currently executing processor. In many cases we must insure that the processor does not change while a code segment is executed. __this_cpu_ptr -> Do not check for preemption context this_cpu_ptr -> Check preemption context The parameter to these operations is a per cpu pointer. This can be the address of a statically defined per cpu variable (&per_cpu_var(xxx)) or the address of a per cpu variable allocated with the per cpu allocator. per cpu atomic operations: this_cpu_*(var, val) ----------------------------------------------- this_cpu_* operations (like this_cpu_add(struct->y, value) operate on abitrary scalars that are members of structures allocated with the new per cpu allocator. They can also operate on static per_cpu variables if they are passed to per_cpu_var() (See patch to use this_cpu_* operations for vm statistics). These operations are guaranteed to be atomic vs preemption when modifying the scalar. The calculation of the per cpu offset is also guaranteed to be atomic at the same time. This means that a this_cpu_* operation can be safely used to modify a per cpu variable in a context where interrupts are enabled and preemption is allowed. Many architectures can perform such a per cpu atomic operation with a single instruction. Note that the atomicity here is different from regular atomic operations. Atomicity is only guaranteed for data accessed from the currently executing processor. Modifications from other processors are still possible. There must be other guarantees that the per cpu data is not modified from another processor when using these instruction. The per cpu atomicity is created by the fact that the processor either executes and instruction or not. Embedded in the instruction is the relocation of the per cpu address to the are reserved for the current processor and the RMW action. Therefore interrupts or preemption cannot occur in the mids of this processing. Generic fallback functions are used if an arch does not define optimized this_cpu operations. The functions come also come in the two flavors used for this_cpu_ptr(). The firstparameter is a scalar that is a member of a structure allocated through allocpercpu or a per cpu variable (use per_cpu_var(xxx)). The operations are similar to what percpu_add() and friends do. this_cpu_read(scalar) this_cpu_write(scalar, value) this_cpu_add(scale, value) this_cpu_sub(scalar, value) this_cpu_inc(scalar) this_cpu_dec(scalar) this_cpu_and(scalar, value) this_cpu_or(scalar, value) this_cpu_xor(scalar, value) Arch code can override the generic functions and provide optimized atomic per cpu operations. These atomic operations must provide both the relocation (x86 does it through a segment override) and the operation on the data in a single instruction. Otherwise preempt needs to be disabled and there is no gain from providing arch implementations. A third variant is provided prefixed by irqsafe_. These variants are safe against hardware interrupts on the *same* processor (all per cpu atomic primitives are *always* *only* providing safety for code running on the *same* processor!). The increment needs to be implemented by the hardware in such a way that it is a single RMW instruction that is either processed before or after an interrupt. cc: David Howells cc: Ingo Molnar cc: Rusty Russell cc: Eric Dumazet Signed-off-by: Christoph Lameter Signed-off-by: Tejun Heo