perf/x86/intel/pt: Get rid of reverse lookup table for ToPA

In order to quickly find a ToPA entry by its page offset in the buffer,
we're using a reverse lookup table. The problem with it is that it's a
large array of mostly similar pointers, especially so now that we're
using high order allocations from the page allocator. Because its size
is limited to whatever is the maximum for kmalloc(), it places a limit
on the number of ToPA entries per buffer, and therefore, on the total
buffer size, which otherwise doesn't have to be there.

Replace the reverse lookup table with a simple runtime lookup. With the
high order AUX allocations in place, the runtime penalty of such a lookup
is much smaller and in cases where all entries in a ToPA table are of
the same size, the complexity is O(1).

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: http://lkml.kernel.org/r/20190821124727.73310-7-alexander.shishkin@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 6 insertions, 4 deletions

diff --git a/arch/x86/events/intel/pt.h b/arch/x86/events/intel/pt.h
index 8de8ed089697..1d2bb7572374 100644
--- a/arch/x86/events/intel/pt.h
+++ b/arch/x86/events/intel/pt.h
@@ -64,8 +64,10 @@ struct pt_pmu {
  * @lost:	if data was lost/truncated
  * @head:	logical write offset inside the buffer
  * @snapshot:	if this is for a snapshot/overwrite counter
- * @stop_pos:	STOP topa entry in the buffer
- * @intr_pos:	INT topa entry in the buffer
+ * @stop_pos:	STOP topa entry index
+ * @intr_pos:	INT topa entry index
+ * @stop_te:	STOP topa entry pointer
+ * @intr_te:	INT topa entry pointer
  * @data_pages:	array of pages from perf
  * @topa_index:	table of topa entries indexed by page offset
  */
@@ -78,9 +80,9 @@ struct pt_buffer {
 	local_t			data_size;
 	local64_t		head;
 	bool			snapshot;
-	unsigned long		stop_pos, intr_pos;
+	long			stop_pos, intr_pos;
+	struct topa_entry	*stop_te, *intr_te;
 	void			**data_pages;
-	struct topa_entry	*topa_index[0];
 };
 
 #define PT_FILTERS_NUM	4