1. 11 Feb, 2009 3 commits
    • Arnaldo Carvalho de Melo's avatar
      ring_buffer: pahole struct ring_buffer · 00f62f61
      Arnaldo Carvalho de Melo authored
      While fixing some bugs in pahole (built-in.o files were not being
      processed due to relocation problems) I found out about these packable
      structures:
      
      $ pahole --packable kernel/trace/ring_buffer.o  | grep ring
      ring_buffer	72	64	8
      ring_buffer_per_cpu	112	104	8
      
      If we take a look at the current layout of struct ring_buffer we can see
      that we have two 4 bytes holes.
      
      $ pahole -C ring_buffer kernel/trace/ring_buffer.o
      struct ring_buffer {
      	unsigned int               pages;           /*     0     4 */
      	unsigned int               flags;           /*     4     4 */
      	int                        cpus;            /*     8     4 */
      
      	/* XXX 4 bytes hole, try to pack */
      
      	cpumask_var_t              cpumask;         /*    16     8 */
      	atomic_t                   record_disabled; /*    24     4 */
      
      	/* XXX 4 bytes hole, try to pack */
      
      	struct mutex               mutex;           /*    32    32 */
      	/* --- cacheline 1 boundary (64 bytes) --- */
      	struct ring_buffer_per_cpu * * buffers;     /*    64     8 */
      
      	/* size: 72, cachelines: 2, members: 7 */
      	/* sum members: 64, holes: 2, sum holes: 8 */
      	/* last cacheline: 8 bytes */
      };
      
      So, if I ask pahole to reorganize it:
      
      $ pahole -C ring_buffer --reorganize kernel/trace/ring_buffer.o
      
      struct ring_buffer {
      	unsigned int               pages;           /*     0     4 */
      	unsigned int               flags;           /*     4     4 */
      	int                        cpus;            /*     8     4 */
      	atomic_t                   record_disabled; /*    12     4 */
      	cpumask_var_t              cpumask;         /*    16     8 */
      	struct mutex               mutex;           /*    24    32 */
      	struct ring_buffer_per_cpu * * buffers;     /*    56     8 */
      	/* --- cacheline 1 boundary (64 bytes) --- */
      
      	/* size: 64, cachelines: 1, members: 7 */
      };   /* saved 8 bytes and 1 cacheline! */
      
      We get it using just one 64 bytes cacheline.
      
      To see what it did:
      
      $ pahole -C ring_buffer --reorganize --show_reorg_steps \
      	kernel/trace/ring_buffer.o | grep \/
      /* Moving 'record_disabled' from after 'cpumask' to after 'cpus' */
      Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
      Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      00f62f61
    • Ingo Molnar's avatar
    • Ingo Molnar's avatar
      Merge branch 'tip/tracing/urgent' of... · 7d6d49b1
      Ingo Molnar authored
      Merge branch 'tip/tracing/urgent' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace into tracing/urgent
      7d6d49b1
  2. 10 Feb, 2009 3 commits
  3. 09 Feb, 2009 34 commits