Commit-ID: 5b1dbd17c0dee679b154ce47f534677b7e0f7ad6
Gitweb: http://git.kernel.org/tip/5b1dbd17c0dee679b154ce47f534677b7e0f7ad6
Author: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
AuthorDate: Tue, 21 Apr 2015 16:16:16 +0300
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 27 May 2015 09:17:47 +0200
perf/x86/intel/pt: Document pt_buffer_reset_offsets()
Currently, the description of pt_buffer_reset_offsets() lacks information
about its calling constraints and ordering with regards to other buffer
management functions.
Add a clarification about when this function has to be called.
Signed-off-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: acme@xxxxxxxxxxxxx
Cc: adrian.hunter@xxxxxxxxx
Cc: hpa@xxxxxxxxx
Link: http://lkml.kernel.org/r/1429622177-22843-5-git-send-email-alexander.shishkin@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/kernel/cpu/perf_event_intel_pt.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/cpu/perf_event_intel_pt.c b/arch/x86/kernel/cpu/perf_event_intel_pt.c
index b2746ea..40ba5e4 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_pt.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_pt.c
@@ -705,7 +705,14 @@ static void pt_buffer_setup_topa_index(struct pt_buffer *buf)
* @head: Write pointer (aux_head) from AUX buffer.
*
* Find the ToPA table and entry corresponding to given @head and set buffer's
- * "current" pointers accordingly.
+ * "current" pointers accordingly. This is done after we have obtained the
+ * current aux_head position from a successful call to perf_aux_output_begin()
+ * to make sure the hardware is writing to the right place.
+ *
+ * This function modifies buf::{cur,cur_idx,output_off} that will be programmed
+ * into PT msrs when the tracing is enabled and buf::head and buf::data_size,
+ * which are used to determine INT and STOP markers' locations by a subsequent
+ * call to pt_buffer_reset_markers().
*/
static void pt_buffer_reset_offsets(struct pt_buffer *buf, unsigned long head)
{
--
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