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authorSteven Rostedt <srostedt@redhat.com>2010-03-18 17:54:19 -0400
committerSteven Rostedt <rostedt@goodmis.org>2010-03-18 23:11:35 -0400
commit2271048d1b3b0aabf83d25b29c20646dcabedc05 (patch)
tree4d20fa61a1d6fc2542b283b45c2a7a374fb2c3f5 /kernel/trace/ring_buffer.c
parenta3d3203e4bb40f253b1541e310dc0f9305be7c84 (diff)
ring-buffer: Do 8 byte alignment for 64 bit that can not handle 4 byte align
The ring buffer uses 4 byte alignment while recording events into the buffer, even on 64bit machines. This saves space when there are lots of events being recorded at 4 byte boundaries. The ring buffer has a zero copy method to write into the buffer, with the reserving of space and then committing it. This may cause problems when writing an 8 byte word into a 4 byte alignment (not 8). For x86 and PPC this is not an issue, but on some architectures this would cause an out-of-alignment exception. This patch uses CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS to determine if it is OK to use 4 byte alignments on 64 bit machines. If it is not, it forces the ring buffer event header to be 8 bytes and not 4, and will align the length of the data to be 8 byte aligned. This keeps the data payload at 8 byte alignments and will allow these machines to run without issue. The trick to this is that the header can be either 4 bytes or 8 bytes depending on the length of the data payload. The 4 byte header has a length field that supports up to 112 bytes. If the length of the data is more than 112, the length field is set to zero, and the actual length is stored in the next 4 bytes after the header. When CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS is not set, the code forces zero in the 4 byte header forcing the length to be stored in the 4 byte array, even with a small data load. It also forces the length of the data load to be 8 byte aligned. The combination of these two guarantee that the data is always at 8 byte alignment. Tested-by: Frederic Weisbecker <fweisbec@gmail.com> (on sparc64) Reported-by: Frederic Weisbecker <fweisbec@gmail.com> Acked-by: David S. Miller <davem@davemloft.net> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace/ring_buffer.c')
-rw-r--r--kernel/trace/ring_buffer.c14
1 files changed, 11 insertions, 3 deletions
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 05a9f83b8819..d1187ef20caf 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -207,6 +207,14 @@ EXPORT_SYMBOL_GPL(tracing_is_on);
207#define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX) 207#define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
208#define RB_EVNT_MIN_SIZE 8U /* two 32bit words */ 208#define RB_EVNT_MIN_SIZE 8U /* two 32bit words */
209 209
210#if !defined(CONFIG_64BIT) || defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
211# define RB_FORCE_8BYTE_ALIGNMENT 0
212# define RB_ARCH_ALIGNMENT RB_ALIGNMENT
213#else
214# define RB_FORCE_8BYTE_ALIGNMENT 1
215# define RB_ARCH_ALIGNMENT 8U
216#endif
217
210/* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */ 218/* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
211#define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX 219#define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
212 220
@@ -1547,7 +1555,7 @@ rb_update_event(struct ring_buffer_event *event,
1547 1555
1548 case 0: 1556 case 0:
1549 length -= RB_EVNT_HDR_SIZE; 1557 length -= RB_EVNT_HDR_SIZE;
1550 if (length > RB_MAX_SMALL_DATA) 1558 if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT)
1551 event->array[0] = length; 1559 event->array[0] = length;
1552 else 1560 else
1553 event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT); 1561 event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
@@ -1722,11 +1730,11 @@ static unsigned rb_calculate_event_length(unsigned length)
1722 if (!length) 1730 if (!length)
1723 length = 1; 1731 length = 1;
1724 1732
1725 if (length > RB_MAX_SMALL_DATA) 1733 if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT)
1726 length += sizeof(event.array[0]); 1734 length += sizeof(event.array[0]);
1727 1735
1728 length += RB_EVNT_HDR_SIZE; 1736 length += RB_EVNT_HDR_SIZE;
1729 length = ALIGN(length, RB_ALIGNMENT); 1737 length = ALIGN(length, RB_ARCH_ALIGNMENT);
1730 1738
1731 return length; 1739 return length;
1732} 1740}