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perf/x86/intel/pt: Document pt_buffer_reset_offsets()

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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@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: acme@infradead.org
Cc: adrian.hunter@intel.com
Cc: hpa@zytor.com
Link: http://lkml.kernel.org/r/1429622177-22843-5-git-send-email-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Alexander Shishkin 2015-04-21 16:16:16 +03:00 committed by Ingo Molnar
parent cf302bfdf3
commit 5b1dbd17c0
1 changed files with 8 additions and 1 deletions
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9
arch/x86/kernel/cpu/perf_event_intel_pt.c
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@ -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)
{