Trace-events for mtd

Add tracepoints to mtd subsystem for read and write operations. This should allow us to identify applications which are generating too much reads/writes on a flash-device.

Signed-off-by Daniel Walter <[email protected]>

---
 drivers/mtd/mtdcore.c      |  6 +++++-
 include/trace/events/mtd.h | 45 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+), 1 deletion(-)
 create mode 100644 include/trace/events/mtd.h

drivers/mtd/mtdcore.c +5 -1

index 8bbbb75..8f85bfb 100644
@@ -43,6 +43,9 @@
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/partitions.h>
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/mtd.h>
+
 #include "mtdcore.h"
 
 static struct backing_dev_info mtd_bdi = {

@@ -882,7 +885,7 @@ int mtd_read(struct mtd_info *mtd, loff_t from, size_t len, size_t *retlen,
                return -EINVAL;
        if (!len)
                return 0;
-
+       trace_mtd_read(current, len);
        /*
         * In the absence of an error, drivers return a non-negative integer
         * representing the maximum number of bitflips that were corrected on

@@ -907,6 +910,7 @@ int mtd_write(struct mtd_info *mtd, loff_t to, size_t len, size_t *retlen,
                return -EROFS;
        if (!len)
                return 0;
+       trace_mtd_write(current, len);
        return mtd->_write(mtd, to, len, retlen, buf);
 }
 EXPORT_SYMBOL_GPL(mtd_write);

include/trace/events/mtd.h new file +35 -0

new file mode 100644
index 0000000..7191b72
@@ -0,0 +1,45 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM mtd
+
+#if !defined(_TRACE_MTD_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_MTD_H
+
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(mtd_read,
+       TP_PROTO(struct task_struct *task, size_t rlen),
+       TP_ARGS(task, rlen),
+       TP_STRUCT__entry(
+               __field(pid_t, pid)
+               __array(char, comm, TASK_COMM_LEN)
+               __field(size_t, rlen)
+       ),
+       TP_fast_assign(
+               __entry->pid = task->pid;
+               memcpy(__entry->comm, task->comm, TASK_COMM_LEN);
+               __entry->rlen = rlen;
+       ),
+       TP_printk("pid=%d comm=%s rlen=%zu",
+               __entry->pid, __entry->comm, __entry->rlen)
+);
+
+TRACE_EVENT(mtd_write,
+       TP_PROTO(struct task_struct *task, size_t wlen),
+       TP_ARGS(task, wlen),
+       TP_STRUCT__entry(
+               __field(pid_t, pid)
+               __array(char, comm, TASK_COMM_LEN)
+               __field(size_t, wlen)
+       ),
+       TP_fast_assign(
+               __entry->pid = task->pid;

Quoted 5 lines · Daniel Walter

Add tracepoints to mtd subsystem for read and write operations. This should allow us to identify applications which are generating too much reads/writes on a flash-device.

Signed-off-by Daniel Walter <[email protected]>

Brian, any comments on this?

Quoted 8 lines · Richard Weinberger

Quoted 5 lines · Daniel Walter

Add tracepoints to mtd subsystem for read and write operations. This should allow us to identify applications which are generating too much reads/writes on a flash-device.

Signed-off-by Daniel Walter <[email protected]>

Brian, any comments on this?

Only a few. I'm not very familiar with writing trace events. I've only barely used them! And I haven't run this patch yet.

But I thought Daniel reported having some difficulty here -- that it isn't actually that useful to get real "user" information, since most writing/erasing happens from background UBI tasks in practice. So is this still the best mechanism for tracking this information? (Even if there's better ways to get info directly out of UBI, I guess maybe it'd still be good to have this infrastructure.)

Also, maybe I'm missing something, but it doesn't look like this attempts to record *which* MTD is being accessed, right? I'd think logging mtd->name could help?

Brian

I wanted to reach out to the broader community to find out if I missed somethings and to get overall feedback if more traceevents would be useful to help us debugging mtd i/o a little bit better.