| Message ID | 20110121203643.046218322@efficios.com |
|---|---|
| State | Not Applicable |
| Delegated to: | David Miller |
| Headers | show |
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Date: Fri, 21 Jan 2011 15:36:33 -0500 > commit 7e066fb870fcd1025ec3ba7bbde5d541094f4ce1 added the aligned(32) type and > variable attribute to the tracepoint structures to deal with gcc happily > aligning statically defined structures on 32-byte multiples. > > Working on issues within Ftrace, we came up with __64_aligned, which deals with > this issue more elegantly by forcing an 8-byte alignment to both the type > declaration and variable definition. > > This therefore saves space, bringing down the size of struct tracepoint from 64 > bytes to 38 on 64-bit architectures. > > Updating: > - The type attribute (for iteration over the struct tracepoint array) > - Added the variable attribute to the extern definition (needed to force gcc to > consider this alignment for the following definition) > - The definition variable attribute (to force gcc to this specific alignment for > the static definitions) > - The linker script (8-byte alignment can now replace the previous 32-byte > alignment for the custom tracepoint section) > > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Acked-by: David S. Miller <davem@davemloft.net> -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Index: linux-2.6-lttng/include/asm-generic/vmlinux.lds.h =================================================================== --- linux-2.6-lttng.orig/include/asm-generic/vmlinux.lds.h +++ linux-2.6-lttng/include/asm-generic/vmlinux.lds.h @@ -168,7 +168,7 @@ CPU_KEEP(exit.data) \ MEM_KEEP(init.data) \ MEM_KEEP(exit.data) \ - . = ALIGN(32); \ + U64_ALIGN(); \ VMLINUX_SYMBOL(__start___tracepoints) = .; \ *(__tracepoints) \ VMLINUX_SYMBOL(__stop___tracepoints) = .; \ Index: linux-2.6-lttng/include/linux/tracepoint.h =================================================================== --- linux-2.6-lttng.orig/include/linux/tracepoint.h +++ linux-2.6-lttng/include/linux/tracepoint.h @@ -33,12 +33,7 @@ struct tracepoint { void (*regfunc)(void); void (*unregfunc)(void); struct tracepoint_func *funcs; -} __attribute__((aligned(32))); /* - * Aligned on 32 bytes because it is - * globally visible and gcc happily - * align these on the structure size. - * Keep in sync with vmlinux.lds.h. - */ +} __u64_aligned; /* * Connect a probe to a tracepoint. @@ -143,7 +138,7 @@ static inline void tracepoint_update_pro * structure. Force alignment to the same alignment as the section start. */ #define __DECLARE_TRACE(name, proto, args, data_proto, data_args) \ - extern struct tracepoint __tracepoint_##name; \ + extern struct tracepoint __u64_aligned __tracepoint_##name; \ static inline void trace_##name(proto) \ { \ JUMP_LABEL(&__tracepoint_##name.state, do_trace); \ @@ -174,7 +169,8 @@ do_trace: \ static const char __tpstrtab_##name[] \ __attribute__((section("__tracepoints_strings"))) = #name; \ struct tracepoint __tracepoint_##name \ - __attribute__((section("__tracepoints"), aligned(32))) = \ + __u64_aligned \ + __attribute__((section("__tracepoints"))) = \ { __tpstrtab_##name, 0, reg, unreg, NULL } #define DEFINE_TRACE(name) \
commit 7e066fb870fcd1025ec3ba7bbde5d541094f4ce1 added the aligned(32) type and variable attribute to the tracepoint structures to deal with gcc happily aligning statically defined structures on 32-byte multiples. Working on issues within Ftrace, we came up with __64_aligned, which deals with this issue more elegantly by forcing an 8-byte alignment to both the type declaration and variable definition. This therefore saves space, bringing down the size of struct tracepoint from 64 bytes to 38 on 64-bit architectures. Updating: - The type attribute (for iteration over the struct tracepoint array) - Added the variable attribute to the extern definition (needed to force gcc to consider this alignment for the following definition) - The definition variable attribute (to force gcc to this specific alignment for the static definitions) - The linker script (8-byte alignment can now replace the previous 32-byte alignment for the custom tracepoint section) Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> CC: David Miller <davem@davemloft.net> CC: Steven Rostedt <rostedt@goodmis.org> CC: Frederic Weisbecker <fweisbec@gmail.com> CC: Ingo Molnar <mingo@elte.hu> --- include/asm-generic/vmlinux.lds.h | 2 +- include/linux/tracepoint.h | 12 ++++-------- 2 files changed, 5 insertions(+), 9 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe sparclinux" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html