* [PATCH][GIT PULL][v2.6.34] ring-buffer: Do 8 byte alignment for 64 bit that can not handle 4 byte align
@ 2010-03-19 2:44 Steven Rostedt
2010-03-19 3:03 ` David Miller
0 siblings, 1 reply; 4+ messages in thread
From: Steven Rostedt @ 2010-03-19 2:44 UTC (permalink / raw)
To: LKML
Cc: Ingo Molnar, Andrew Morton, Frederic Weisbecker, Sparc,
David Miller, Tejun Heo
Ingo,
This patch fixes a bug in the ring buffer that breaks 64bit boxes that
can not write a long on a 4byte alignment.
Please pull the latest tip/tracing/urgent tree, which can be found at:
git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
tip/tracing/urgent
Steven Rostedt (1):
ring-buffer: Do 8 byte alignment for 64 bit that can not handle 4 byte align
----
kernel/trace/ring_buffer.c | 14 +++++++++++---
1 files changed, 11 insertions(+), 3 deletions(-)
---------------------------
commit fb6b926d6be02e0767c92cbde4c8574f6a9eca27
Author: Steven Rostedt <srostedt@redhat.com>
Date: Thu Mar 18 17:54:19 2010 -0400
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>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 05a9f83..d1187ef 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -207,6 +207,14 @@ EXPORT_SYMBOL_GPL(tracing_is_on);
#define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
#define RB_EVNT_MIN_SIZE 8U /* two 32bit words */
+#if !defined(CONFIG_64BIT) || defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
+# define RB_FORCE_8BYTE_ALIGNMENT 0
+# define RB_ARCH_ALIGNMENT RB_ALIGNMENT
+#else
+# define RB_FORCE_8BYTE_ALIGNMENT 1
+# define RB_ARCH_ALIGNMENT 8U
+#endif
+
/* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
#define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
@@ -1547,7 +1555,7 @@ rb_update_event(struct ring_buffer_event *event,
case 0:
length -= RB_EVNT_HDR_SIZE;
- if (length > RB_MAX_SMALL_DATA)
+ if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT)
event->array[0] = length;
else
event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
@@ -1722,11 +1730,11 @@ static unsigned rb_calculate_event_length(unsigned length)
if (!length)
length = 1;
- if (length > RB_MAX_SMALL_DATA)
+ if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT)
length += sizeof(event.array[0]);
length += RB_EVNT_HDR_SIZE;
- length = ALIGN(length, RB_ALIGNMENT);
+ length = ALIGN(length, RB_ARCH_ALIGNMENT);
return length;
}
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH][GIT PULL][v2.6.34] ring-buffer: Do 8 byte alignment for 64 bit that can not handle 4 byte align
2010-03-19 2:44 [PATCH][GIT PULL][v2.6.34] ring-buffer: Do 8 byte alignment for 64 bit that can not handle 4 byte align Steven Rostedt
@ 2010-03-19 3:03 ` David Miller
2010-03-19 3:15 ` [PATCH v2][GIT " Steven Rostedt
0 siblings, 1 reply; 4+ messages in thread
From: David Miller @ 2010-03-19 3:03 UTC (permalink / raw)
To: rostedt; +Cc: linux-kernel, mingo, akpm, fweisbec, sparclinux, tj
From: Steven Rostedt <rostedt@goodmis.org>
Date: Thu, 18 Mar 2010 22:44:17 -0400
> Tested-by: Frederic Weisbecker <fweisbec@gmail.com>
> (on sparc64)
> Reported-by: Frederic Weisbecker <fweisbec@gmail.com>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: David S. Miller <davem@davemloft.net>
^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH v2][GIT PULL][v2.6.34] ring-buffer: Do 8 byte alignment for 64 bit that can not handle 4 byte align
2010-03-19 3:03 ` David Miller
@ 2010-03-19 3:15 ` Steven Rostedt
2010-03-19 7:41 ` Ingo Molnar
0 siblings, 1 reply; 4+ messages in thread
From: Steven Rostedt @ 2010-03-19 3:15 UTC (permalink / raw)
To: LKML; +Cc: David Miller, mingo, akpm, fweisbec, sparclinux, tj
Rebased to add David's ACK.
Ingo,
Please pull the latest tip/tracing/urgent tree, which can be found at:
git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
tip/tracing/urgent
Steven Rostedt (1):
ring-buffer: Do 8 byte alignment for 64 bit that can not handle 4 byte align
----
kernel/trace/ring_buffer.c | 14 +++++++++++---
1 files changed, 11 insertions(+), 3 deletions(-)
---------------------------
commit 2271048d1b3b0aabf83d25b29c20646dcabedc05
Author: Steven Rostedt <srostedt@redhat.com>
Date: Thu Mar 18 17:54:19 2010 -0400
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>
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 05a9f83..d1187ef 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -207,6 +207,14 @@ EXPORT_SYMBOL_GPL(tracing_is_on);
#define RB_MAX_SMALL_DATA (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
#define RB_EVNT_MIN_SIZE 8U /* two 32bit words */
+#if !defined(CONFIG_64BIT) || defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
+# define RB_FORCE_8BYTE_ALIGNMENT 0
+# define RB_ARCH_ALIGNMENT RB_ALIGNMENT
+#else
+# define RB_FORCE_8BYTE_ALIGNMENT 1
+# define RB_ARCH_ALIGNMENT 8U
+#endif
+
/* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
#define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
@@ -1547,7 +1555,7 @@ rb_update_event(struct ring_buffer_event *event,
case 0:
length -= RB_EVNT_HDR_SIZE;
- if (length > RB_MAX_SMALL_DATA)
+ if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT)
event->array[0] = length;
else
event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
@@ -1722,11 +1730,11 @@ static unsigned rb_calculate_event_length(unsigned length)
if (!length)
length = 1;
- if (length > RB_MAX_SMALL_DATA)
+ if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT)
length += sizeof(event.array[0]);
length += RB_EVNT_HDR_SIZE;
- length = ALIGN(length, RB_ALIGNMENT);
+ length = ALIGN(length, RB_ARCH_ALIGNMENT);
return length;
}
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2][GIT PULL][v2.6.34] ring-buffer: Do 8 byte alignment for 64 bit that can not handle 4 byte align
2010-03-19 3:15 ` [PATCH v2][GIT " Steven Rostedt
@ 2010-03-19 7:41 ` Ingo Molnar
0 siblings, 0 replies; 4+ messages in thread
From: Ingo Molnar @ 2010-03-19 7:41 UTC (permalink / raw)
To: Steven Rostedt; +Cc: LKML, David Miller, akpm, fweisbec, sparclinux, tj
* Steven Rostedt <rostedt@goodmis.org> wrote:
> Rebased to add David's ACK.
>
> Ingo,
>
> Please pull the latest tip/tracing/urgent tree, which can be found at:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
> tip/tracing/urgent
>
>
> Steven Rostedt (1):
> ring-buffer: Do 8 byte alignment for 64 bit that can not handle 4 byte align
Pulled, thanks a lot Steve!
Ingo
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2010-03-19 7:41 UTC | newest]
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2010-03-19 2:44 [PATCH][GIT PULL][v2.6.34] ring-buffer: Do 8 byte alignment for 64 bit that can not handle 4 byte align Steven Rostedt
2010-03-19 3:03 ` David Miller
2010-03-19 3:15 ` [PATCH v2][GIT " Steven Rostedt
2010-03-19 7:41 ` Ingo Molnar
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