On Mon, 26 Aug 2013 20:44:37 +0000 Christoph Lameter <[email protected]> wrote:
> __get_cpu_var() is used for multiple purposes in the kernel source. One of > them is > address calculation via the form &__get_cpu_var(x). This calculates the > address for > the instance of the percpu variable of the current processor based on an > offset. > > Others usage cases are for storing and retrieving data from the current > processors percpu area. > __get_cpu_var() can be used as an lvalue when writing data or on the right > side of an assignment. > > __get_cpu_var() is defined as : > > > #define __get_cpu_var(var) (*this_cpu_ptr(&(var))) > > > > __get_cpu_var() always only does a address determination. However, store and > retrieve operations > could use a segment prefix (or global register on other platforms) to avoid > the address calculation. > > this_cpu_write() and this_cpu_read() can directly take an offset into a > percpu area and use > optimized assembly code to read and write per cpu variables. > > > This patch converts __get_cpu_var into either and explicit address > calculation using this_cpu_ptr() > or into a use of this_cpu operations that use the offset. Thereby address > calcualtions are avoided > and less registers are used when code is generated. > > At the end of the patchset all uses of __get_cpu_var have been removed so the > macro is removed too. > > The patchset includes passes over all arches as well. Once these operations > are used throughout then > specialized macros can be defined in non -x86 arches as well in order to > optimize per cpu access by > f.e. using a global register that may be set to the per cpu base. You should limit the width of the change log to 76 characters. I fixed it for now. > > > > > Transformations done to __get_cpu_var() > > > 1. Determine the address of the percpu instance of the current processor. > > DEFINE_PER_CPU(int, y); > int *x = &__get_cpu_var(y); > > Converts to > > int *x = this_cpu_ptr(&y); > > > 2. Same as #1 but this time an array structure is involved. > > DEFINE_PER_CPU(int, y[20]); > int *x = __get_cpu_var(y); > > Converts to > > int *x = this_cpu_ptr(y); > > > 3. Retrieve the content of the current processors instance of a per cpu > variable. > > DEFINE_PER_CPU(int, u); > int x = __get_cpu_var(y) > > Converts to > > int x = __this_cpu_read(y); > > > 4. Retrieve the content of a percpu struct > > DEFINE_PER_CPU(struct mystruct, y); > struct mystruct x = __get_cpu_var(y); > > Converts to > > memcpy(this_cpu_ptr(&y), x, sizeof(x)); > > > 5. Assignment to a per cpu variable > > DEFINE_PER_CPU(int, y) > __get_cpu_var(y) = x; > > Converts to > > this_cpu_write(y, x); > > > 6. Increment/Decrement etc of a per cpu variable > > DEFINE_PER_CPU(int, y); > __get_cpu_var(y)++ > > Converts to > > this_cpu_inc(y) > > > Signed-off-by: Christoph Lameter <[email protected]> > > Index: linux/include/linux/kprobes.h > =================================================================== > --- linux.orig/include/linux/kprobes.h 2013-08-26 14:25:53.000000000 > -0500 > +++ linux/include/linux/kprobes.h 2013-08-26 14:26:29.460993659 -0500 > @@ -329,7 +329,7 @@ static inline void reset_current_kprobe( > > static inline struct kprobe_ctlblk *get_kprobe_ctlblk(void) > { > - return (&__get_cpu_var(kprobe_ctlblk)); > + return this_cpu_ptr(&kprobe_ctlblk); > } Masami, Can you give me an Acked-by: for this. Thanks! -- Steve > > int register_kprobe(struct kprobe *p); > Index: linux/kernel/trace/ftrace.c > =================================================================== > --- linux.orig/kernel/trace/ftrace.c 2013-08-26 14:25:53.000000000 -0500 > +++ linux/kernel/trace/ftrace.c 2013-08-26 14:26:29.460993659 -0500 > @@ -870,7 +870,7 @@ function_profile_call(unsigned long ip, > > local_irq_save(flags); > > - stat = &__get_cpu_var(ftrace_profile_stats); > + stat = this_cpu_ptr(&ftrace_profile_stats); > if (!stat->hash || !ftrace_profile_enabled) > goto out; > > @@ -901,7 +901,7 @@ static void profile_graph_return(struct > unsigned long flags; > > local_irq_save(flags); > - stat = &__get_cpu_var(ftrace_profile_stats); > + stat = this_cpu_ptr(&ftrace_profile_stats); > if (!stat->hash || !ftrace_profile_enabled) > goto out; > > Index: linux/kernel/trace/trace.c > =================================================================== > --- linux.orig/kernel/trace/trace.c 2013-08-26 14:25:53.000000000 -0500 > +++ linux/kernel/trace/trace.c 2013-08-26 14:26:29.464993617 -0500 > @@ -1676,7 +1676,7 @@ static void __ftrace_trace_stack(struct > */ > barrier(); > if (use_stack == 1) { > - trace.entries = &__get_cpu_var(ftrace_stack).calls[0]; > + trace.entries = this_cpu_ptr(ftrace_stack.calls); > trace.max_entries = FTRACE_STACK_MAX_ENTRIES; > > if (regs) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
