Messages in this thread | | | From | Nadav Amit <> | Subject | Re: [RESEND][PATCH v3 06/17] static_call: Add basic static call infrastructure | Date | Thu, 26 Mar 2020 16:42:07 +0000 |
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> On Mar 24, 2020, at 6:56 AM, Peter Zijlstra <peterz@infradead.org> wrote: > > Static calls are a replacement for global function pointers. They use > code patching to allow direct calls to be used instead of indirect > calls. They give the flexibility of function pointers, but with > improved performance. This is especially important for cases where > retpolines would otherwise be used, as retpolines can significantly > impact performance. > > The concept and code are an extension of previous work done by Ard > Biesheuvel and Steven Rostedt: > > https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.kernel.org%2Fr%2F20181005081333.15018-1-ard.biesheuvel%40linaro.org&data=02%7C01%7Cnamit%40vmware.com%7C48cb49e3bd65479a440008d7cfff207d%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C637206567005697724&sdata=jLAdeYFX8C67QFeYtiguq9BfeN8zxjSa8gmtY%2F2nJQ8%3D&reserved=0 > https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.kernel.org%2Fr%2F20181006015110.653946300%40goodmis.org&data=02%7C01%7Cnamit%40vmware.com%7C48cb49e3bd65479a440008d7cfff207d%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C637206567005697724&sdata=KBVx7EJo4EgzKaCccAaMP7C4L%2BYlQ6liO4wO7vv27MU%3D&reserved=0 > > There are two implementations, depending on arch support: > > 1) out-of-line: patched trampolines (CONFIG_HAVE_STATIC_CALL) > 2) basic function pointers > > For more details, see the comments in include/linux/static_call.h. > > [peterz: simplified interface] > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- > arch/Kconfig | 3 > include/linux/static_call.h | 137 ++++++++++++++++++++++++++++++++++++++ > include/linux/static_call_types.h | 15 ++++ > 3 files changed, 155 insertions(+) > create mode 100644 include/linux/static_call.h > create mode 100644 include/linux/static_call_types.h > > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -941,6 +941,9 @@ config HAVE_SPARSE_SYSCALL_NR > entries at 4000, 5000 and 6000 locations. This option turns on syscall > related optimizations for a given architecture. > > +config HAVE_STATIC_CALL > + bool > + > source "kernel/gcov/Kconfig" > > source "scripts/gcc-plugins/Kconfig" > --- /dev/null > +++ b/include/linux/static_call.h > @@ -0,0 +1,137 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +#ifndef _LINUX_STATIC_CALL_H > +#define _LINUX_STATIC_CALL_H > + > +/* > + * Static call support > + * > + * Static calls use code patching to hard-code function pointers into direct > + * branch instructions. They give the flexibility of function pointers, but > + * with improved performance. This is especially important for cases where > + * retpolines would otherwise be used, as retpolines can significantly impact > + * performance. > + * > + * > + * API overview: > + * > + * DECLARE_STATIC_CALL(name, func); > + * DEFINE_STATIC_CALL(name, func); > + * static_call(name)(args...); > + * static_call_update(name, func); > + * > + * Usage example: > + * > + * # Start with the following functions (with identical prototypes): > + * int func_a(int arg1, int arg2); > + * int func_b(int arg1, int arg2); > + * > + * # Define a 'my_name' reference, associated with func_a() by default > + * DEFINE_STATIC_CALL(my_name, func_a);
Do you want to support optional function attributes, such as “pure” and “const”?
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