[PATCH] module: remove 64 bit alignment padding from struct module with CONFIG_TRACE*

[PATCH] module: remove 64 bit alignment padding from struct module with CONFIG_TRACE*

[Richard Kennedy]

Reorder struct module to remove 24 bytes of alignment padding on 64 bit
builds when the CONFIG_TRACE options are selected. This allows the
structure to fit into one fewer cache lines, and its size drops from 592
to 568 on x86_64.

Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk>

----
patch against v2.6.38-rc4
compiled and tested on x86_64

This change doesn't help in all combinations of selected CONFIGs but
will reduce the maximum size when all of them are set.

regards
Richard


diff --git a/include/linux/module.h b/include/linux/module.h
index 9bdf27c..738d22e 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -367,34 +367,35 @@ struct module
 	struct module_notes_attrs *notes_attrs;
 #endif
 
+	/* The command line arguments (may be mangled).  People like
+	   keeping pointers to this stuff */
+	char *args;
+
 #ifdef CONFIG_SMP
 	/* Per-cpu data. */
 	void __percpu *percpu;
 	unsigned int percpu_size;
 #endif
 
-	/* The command line arguments (may be mangled).  People like
-	   keeping pointers to this stuff */
-	char *args;
 #ifdef CONFIG_TRACEPOINTS
-	struct tracepoint * const *tracepoints_ptrs;
 	unsigned int num_tracepoints;
+	struct tracepoint * const *tracepoints_ptrs;
 #endif
 #ifdef HAVE_JUMP_LABEL
 	struct jump_entry *jump_entries;
 	unsigned int num_jump_entries;
 #endif
 #ifdef CONFIG_TRACING
-	const char **trace_bprintk_fmt_start;
 	unsigned int num_trace_bprintk_fmt;
+	const char **trace_bprintk_fmt_start;
 #endif
 #ifdef CONFIG_EVENT_TRACING
 	struct ftrace_event_call **trace_events;
 	unsigned int num_trace_events;
 #endif
 #ifdef CONFIG_FTRACE_MCOUNT_RECORD
-	unsigned long *ftrace_callsites;
 	unsigned int num_ftrace_callsites;
+	unsigned long *ftrace_callsites;
 #endif
 
 #ifdef CONFIG_MODULE_UNLOAD

Re: [PATCH] module: remove 64 bit alignment padding from struct module with CONFIG_TRACE*

[Rusty Russell]

On Mon, 21 Feb 2011 13:57:41 +0000, Richard Kennedy <richard@rsk.demon.co.uk> wrote:
> Reorder struct module to remove 24 bytes of alignment padding on 64 bit
> builds when the CONFIG_TRACE options are selected. This allows the
> structure to fit into one fewer cache lines, and its size drops from 592
> to 568 on x86_64.

Thanks, applied.

Cheers,
Rusty.