[PATCH 7/9] readahead: add vfs/readahead tracing event

[Wu Fengguang <fengguang.wu@intel.com>]

[-- Attachment #1: readahead-tracer.patch --]
[-- Type: text/plain, Size: 3853 bytes --]

This is very useful for verifying whether the readahead algorithms are
working to the expectation.

Example output:

# echo 1 > /debug/tracing/events/vfs/readahead/enable
# cp test-file /dev/null
# cat /debug/tracing/trace  # trimmed output
readahead-initial(dev=0:15, ino=100177, req=0+2, ra=0+4-2, async=0) = 4
readahead-subsequent(dev=0:15, ino=100177, req=2+2, ra=4+8-8, async=1) = 8
readahead-subsequent(dev=0:15, ino=100177, req=4+2, ra=12+16-16, async=1) = 16
readahead-subsequent(dev=0:15, ino=100177, req=12+2, ra=28+32-32, async=1) = 32
readahead-subsequent(dev=0:15, ino=100177, req=28+2, ra=60+60-60, async=1) = 24
readahead-subsequent(dev=0:15, ino=100177, req=60+2, ra=120+60-60, async=1) = 0

CC: Ingo Molnar <mingo@elte.hu>
CC: Jens Axboe <axboe@kernel.dk>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
 include/trace/events/vfs.h |   64 +++++++++++++++++++++++++++++++++++
 mm/readahead.c             |    5 ++
 2 files changed, 69 insertions(+)

--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-next/include/trace/events/vfs.h	2011-11-29 20:58:59.000000000 +0800
@@ -0,0 +1,64 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM vfs
+
+#if !defined(_TRACE_VFS_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_VFS_H
+
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(readahead,
+	TP_PROTO(struct address_space *mapping,
+		 pgoff_t offset,
+		 unsigned long req_size,
+		 enum readahead_pattern pattern,
+		 pgoff_t start,
+		 unsigned long size,
+		 unsigned long async_size,
+		 unsigned int actual),
+
+	TP_ARGS(mapping, offset, req_size, pattern, start, size, async_size,
+		actual),
+
+	TP_STRUCT__entry(
+		__field(	dev_t,		dev		)
+		__field(	ino_t,		ino		)
+		__field(	pgoff_t,	offset		)
+		__field(	unsigned long,	req_size	)
+		__field(	unsigned int,	pattern		)
+		__field(	pgoff_t,	start		)
+		__field(	unsigned int,	size		)
+		__field(	unsigned int,	async_size	)
+		__field(	unsigned int,	actual		)
+	),
+
+	TP_fast_assign(
+		__entry->dev		= mapping->host->i_sb->s_dev;
+		__entry->ino		= mapping->host->i_ino;
+		__entry->offset		= offset;
+		__entry->req_size	= req_size;
+		__entry->pattern	= pattern;
+		__entry->start		= start;
+		__entry->size		= size;
+		__entry->async_size	= async_size;
+		__entry->actual		= actual;
+	),
+
+	TP_printk("readahead-%s(dev=%d:%d, ino=%lu, "
+		  "req=%lu+%lu, ra=%lu+%d-%d, async=%d) = %d",
+			ra_pattern_names[__entry->pattern],
+			MAJOR(__entry->dev),
+			MINOR(__entry->dev),
+			__entry->ino,
+			__entry->offset,
+			__entry->req_size,
+			__entry->start,
+			__entry->size,
+			__entry->async_size,
+			__entry->start > __entry->offset,
+			__entry->actual)
+);
+
+#endif /* _TRACE_VFS_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
--- linux-next.orig/mm/readahead.c	2011-11-29 20:58:53.000000000 +0800
+++ linux-next/mm/readahead.c	2011-11-29 20:59:20.000000000 +0800
@@ -29,6 +29,9 @@ static const char * const ra_pattern_nam
 	[RA_PATTERN_ALL]                = "all",
 };
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/vfs.h>
+
 /*
  * Initialise a struct file's readahead state.  Assumes that the caller has
  * memset *ra to zero.
@@ -215,6 +218,8 @@ static inline void readahead_event(struc
 				for_mmap, for_metadata,
 				pattern, start, size, async_size, actual);
 #endif
+	trace_readahead(mapping, offset, req_size,
+			pattern, start, size, async_size, actual);
 }
 
 


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