[RFC PATCH 35/76] fscache: read-helper: Add tracepoints

From: David Howells
Date: Fri Nov 20 2020 - 10:11:49 EST

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Add three tracepoints to track the activity of the read helpers:

(1) fscache_support/fscache_read

This logs entry to the read helpers and also expansion of the range in
a readahead request.

(2) fscache_support/fscache_rreq

This logs the progress of fscache_read_request objects which track
read requests. A read request may be a compound of multiple
subrequests.

(3) fscache_support/fscache_sreq

This logs the progress of fscache_read_subrequest objects, which track
the contributions from various sources to a read request.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
---

fs/netfs/read_helper.c | 37 ++++++++
include/linux/netfs.h | 2
include/trace/events/netfs.h | 200 ++++++++++++++++++++++++++++++++++++++++++
3 files changed, 239 insertions(+)
create mode 100644 include/trace/events/netfs.h

diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
index f5185402b504..21d3578c6979 100644
--- a/fs/netfs/read_helper.c
+++ b/fs/netfs/read_helper.c
@@ -16,6 +16,8 @@
#include <linux/netfs.h>
#include <linux/fscache.h>
#include "internal.h"
+#define CREATE_TRACE_POINTS
+#include <trace/events/netfs.h>

MODULE_DESCRIPTION("Network fs support");
MODULE_AUTHOR("Red Hat, Inc.");
@@ -38,6 +40,7 @@ static struct netfs_read_request *netfs_alloc_read_request(
const struct netfs_read_request_ops *ops, void *netfs_priv,
struct file *file)
{
+ static atomic_t debug_ids;
struct netfs_read_request *rreq;

rreq = kzalloc(sizeof(struct netfs_read_request), GFP_KERNEL);
@@ -46,6 +49,7 @@ static struct netfs_read_request *netfs_alloc_read_request(
rreq->netfs_priv = netfs_priv;
rreq->inode = file_inode(file);
rreq->i_size = i_size_read(rreq->inode);
+ rreq->debug_id = atomic_inc_return(&debug_ids);
INIT_LIST_HEAD(&rreq->subrequests);
INIT_WORK(&rreq->work, netfs_rreq_work);
refcount_set(&rreq->usage, 1);
@@ -80,6 +84,7 @@ static void netfs_put_read_request(struct netfs_read_request *rreq)
if (rreq->netfs_priv)
rreq->netfs_ops->cleanup(rreq->mapping, rreq->netfs_priv);
fscache_end_operation(&rreq->cache_resources);
+ trace_netfs_rreq(rreq, netfs_rreq_trace_free);
kfree(rreq);
}
}
@@ -109,6 +114,7 @@ static void netfs_get_read_subrequest(struct netfs_read_subrequest *subreq)

static void __netfs_put_subrequest(struct netfs_read_subrequest *subreq)
{
+ trace_netfs_sreq(subreq, netfs_sreq_trace_free);
netfs_put_read_request(subreq->rreq);
kfree(subreq);
}
@@ -188,6 +194,7 @@ static void netfs_read_from_server(struct netfs_read_request *rreq,
*/
static void netfs_rreq_completed(struct netfs_read_request *rreq)
{
+ trace_netfs_rreq(rreq, netfs_rreq_trace_done);
netfs_rreq_clear_subreqs(rreq);
netfs_put_read_request(rreq);
}
@@ -205,6 +212,8 @@ static void netfs_rreq_unmark_after_write(struct netfs_read_request *rreq)
pgoff_t unlocked = 0;
bool have_unlocked = false;

+ trace_netfs_rreq(rreq, netfs_rreq_trace_unmark);
+
rcu_read_lock();

list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
@@ -236,6 +245,8 @@ static void netfs_rreq_copy_terminated(void *priv, ssize_t transferred_or_error)
else
subreq->error = 0;

+ trace_netfs_sreq(subreq, netfs_sreq_trace_write_term);
+
/* If we decrement nr_wr_ops to 0, the ref belongs to us. */
if (atomic_dec_and_test(&rreq->nr_wr_ops))
netfs_rreq_unmark_after_write(rreq);
@@ -252,6 +263,8 @@ static void netfs_rreq_do_write_to_cache(struct netfs_read_request *rreq)
struct netfs_read_subrequest *subreq, *next, *p;
struct iov_iter iter;

+ trace_netfs_rreq(rreq, netfs_rreq_trace_write);
+
/* We don't want terminating writes trying to wake us up whilst we're
* still going through the list.
*/
@@ -275,6 +288,8 @@ static void netfs_rreq_do_write_to_cache(struct netfs_read_request *rreq)
netfs_put_subrequest(next);
}

+ trace_netfs_sreq(subreq, netfs_sreq_trace_write);
+
iov_iter_xarray(&iter, WRITE, &rreq->mapping->i_pages,
subreq->start, subreq->len);

@@ -342,6 +357,8 @@ static void netfs_rreq_unlock(struct netfs_read_request *rreq)
iopos = 0;
subreq_failed = (subreq->error < 0);

+ trace_netfs_rreq(rreq, netfs_rreq_trace_unlock);
+
rcu_read_lock();
xas_for_each(&xas, page, last_page) {
unsigned int pgpos = (page->index - start_page) * PAGE_SIZE;
@@ -398,6 +415,8 @@ static void netfs_rreq_short_read(struct netfs_read_request *rreq,
__clear_bit(NETFS_SREQ_SHORT_READ, &subreq->flags);
__set_bit(NETFS_SREQ_SEEK_DATA_READ, &subreq->flags);

+ trace_netfs_sreq(subreq, netfs_sreq_trace_resubmit_short);
+
netfs_get_read_subrequest(subreq);
atomic_inc(&rreq->nr_rd_ops);
if (subreq->source == NETFS_READ_FROM_CACHE)
@@ -416,6 +435,8 @@ static bool netfs_rreq_perform_resubmissions(struct netfs_read_request *rreq)

WARN_ON(in_softirq());

+ trace_netfs_rreq(rreq, netfs_rreq_trace_resubmit);
+
/* We don't want terminating submissions trying to wake us up whilst
* we're still going through the list.
*/
@@ -428,6 +449,7 @@ static bool netfs_rreq_perform_resubmissions(struct netfs_read_request *rreq)
break;
subreq->source = NETFS_DOWNLOAD_FROM_SERVER;
subreq->error = 0;
+ trace_netfs_sreq(subreq, netfs_sreq_trace_download_instead);
netfs_get_read_subrequest(subreq);
atomic_inc(&rreq->nr_rd_ops);
netfs_read_from_server(rreq, subreq);
@@ -471,6 +493,8 @@ static void netfs_rreq_is_still_valid(struct netfs_read_request *rreq)
*/
static void netfs_rreq_assess(struct netfs_read_request *rreq)
{
+ trace_netfs_rreq(rreq, netfs_rreq_trace_assess);
+
again:
netfs_rreq_is_still_valid(rreq);

@@ -558,6 +582,8 @@ void netfs_subreq_terminated(struct netfs_read_subrequest *subreq,
set_bit(NETFS_RREQ_WRITE_TO_CACHE, &rreq->flags);

out:
+ trace_netfs_sreq(subreq, netfs_sreq_trace_terminated);
+
/* If we decrement nr_rd_ops to 0, the ref belongs to us. */
u = atomic_dec_return(&rreq->nr_rd_ops);
if (u == 0)
@@ -650,6 +676,7 @@ netfs_rreq_prepare_read(struct netfs_read_request *rreq,

out:
subreq->source = source;
+ trace_netfs_sreq(subreq, netfs_sreq_trace_prepare);
return source;
}

@@ -690,6 +717,7 @@ static bool netfs_rreq_submit_slice(struct netfs_read_request *rreq,

rreq->submitted += subreq->len;

+ trace_netfs_sreq(subreq, netfs_sreq_trace_submit);
switch (source) {
case NETFS_FILL_WITH_ZEROES:
netfs_fill_with_zeroes(rreq, subreq);
@@ -750,6 +778,9 @@ static void netfs_rreq_expand(struct netfs_read_request *rreq,
readahead_expand(ractl, rreq->start, rreq->len);
rreq->start = readahead_pos(ractl);
rreq->len = readahead_length(ractl);
+
+ trace_netfs_read(rreq, readahead_pos(ractl), readahead_length(ractl),
+ netfs_read_trace_expanded);
}
}

@@ -791,6 +822,9 @@ void netfs_readahead(struct readahead_control *ractl,
rreq->start = readahead_pos(ractl);
rreq->len = readahead_length(ractl);

+ trace_netfs_read(rreq, readahead_pos(ractl), readahead_length(ractl),
+ netfs_read_trace_readahead);
+
if (ops->begin_cache_operation)
ops->begin_cache_operation(rreq);
netfs_rreq_expand(rreq, ractl);
@@ -863,6 +897,9 @@ int netfs_readpage(struct file *file,
rreq->start = page->index * PAGE_SIZE;
rreq->len = thp_size(page);

+ trace_netfs_read(rreq, page->index * PAGE_SIZE, thp_size(page),
+ netfs_read_trace_readpage);
+
if (ops->begin_cache_operation)
ops->begin_cache_operation(rreq);
netfs_get_read_request(rreq);
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index f2ffea11ea9b..c4276eb9914d 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -53,6 +53,8 @@ struct netfs_read_request {
struct list_head subrequests; /* Requests to fetch I/O from disk or net */
struct work_struct work;
void *netfs_priv; /* Private data for the netfs */
+ unsigned int debug_id;
+ unsigned int cookie_debug_id;
atomic_t nr_rd_ops; /* Number of read ops in progress */
atomic_t nr_wr_ops; /* Number of write ops in progress */
size_t submitted; /* Amount submitted for I/O so far */
diff --git a/include/trace/events/netfs.h b/include/trace/events/netfs.h
new file mode 100644
index 000000000000..56a734a3fb0d
--- /dev/null
+++ b/include/trace/events/netfs.h
@@ -0,0 +1,200 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Network filesystem support module tracepoints
+ *
+ * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@xxxxxxxxxx)
+ */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM netfs
+
+#if !defined(_TRACE_NETFS_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_NETFS_H
+
+#include <linux/fscache.h>
+#include <linux/tracepoint.h>
+
+/*
+ * Define enums for tracing information.
+ */
+#ifndef __NETFS_DECLARE_TRACE_ENUMS_ONCE_ONLY
+#define __NETFS_DECLARE_TRACE_ENUMS_ONCE_ONLY
+
+enum netfs_read_trace {
+ netfs_read_trace_expanded,
+ netfs_read_trace_readahead,
+ netfs_read_trace_readpage,
+};
+
+enum netfs_rreq_trace {
+ netfs_rreq_trace_assess,
+ netfs_rreq_trace_done,
+ netfs_rreq_trace_free,
+ netfs_rreq_trace_resubmit,
+ netfs_rreq_trace_unlock,
+ netfs_rreq_trace_unmark,
+ netfs_rreq_trace_write,
+};
+
+enum netfs_sreq_trace {
+ netfs_sreq_trace_download_instead,
+ netfs_sreq_trace_free,
+ netfs_sreq_trace_prepare,
+ netfs_sreq_trace_resubmit_short,
+ netfs_sreq_trace_submit,
+ netfs_sreq_trace_terminated,
+ netfs_sreq_trace_write,
+ netfs_sreq_trace_write_term,
+};
+
+#endif
+
+#define netfs_read_traces \
+ EM(netfs_read_trace_expanded, "EXPANDED ") \
+ EM(netfs_read_trace_readahead, "READAHEAD") \
+ E_(netfs_read_trace_readpage, "READPAGE ")
+
+#define netfs_rreq_traces \
+ EM(netfs_rreq_trace_assess, "ASSESS") \
+ EM(netfs_rreq_trace_done, "DONE ") \
+ EM(netfs_rreq_trace_free, "FREE ") \
+ EM(netfs_rreq_trace_resubmit, "RESUBM") \
+ EM(netfs_rreq_trace_unlock, "UNLOCK") \
+ EM(netfs_rreq_trace_unmark, "UNMARK") \
+ E_(netfs_rreq_trace_write, "WRITE ")
+
+#define netfs_sreq_sources \
+ EM(NETFS_FILL_WITH_ZEROES, "ZERO") \
+ EM(NETFS_DOWNLOAD_FROM_SERVER, "DOWN") \
+ EM(NETFS_READ_FROM_CACHE, "READ") \
+ E_(NETFS_INVALID_READ, "INVL") \
+
+#define netfs_sreq_traces \
+ EM(netfs_sreq_trace_download_instead, "RDOWN") \
+ EM(netfs_sreq_trace_free, "FREE ") \
+ EM(netfs_sreq_trace_prepare, "PREP ") \
+ EM(netfs_sreq_trace_resubmit_short, "SHORT") \
+ EM(netfs_sreq_trace_submit, "SUBMT") \
+ EM(netfs_sreq_trace_terminated, "TERM ") \
+ EM(netfs_sreq_trace_write, "WRITE") \
+ E_(netfs_sreq_trace_write_term, "WTERM")
+
+
+/*
+ * Export enum symbols via userspace.
+ */
+#undef EM
+#undef E_
+#define EM(a, b) TRACE_DEFINE_ENUM(a);
+#define E_(a, b) TRACE_DEFINE_ENUM(a);
+
+netfs_read_traces;
+netfs_rreq_traces;
+netfs_sreq_sources;
+netfs_sreq_traces;
+
+/*
+ * Now redefine the EM() and E_() macros to map the enums to the strings that
+ * will be printed in the output.
+ */
+#undef EM
+#undef E_
+#define EM(a, b) { a, b },
+#define E_(a, b) { a, b }
+
+TRACE_EVENT(netfs_read,
+ TP_PROTO(struct netfs_read_request *rreq,
+ loff_t start, size_t len,
+ enum netfs_read_trace what),
+
+ TP_ARGS(rreq, start, len, what),
+
+ TP_STRUCT__entry(
+ __field(unsigned int, rreq )
+ __field(unsigned int, cookie )
+ __field(loff_t, start )
+ __field(size_t, len )
+ __field(enum netfs_read_trace, what )
+ ),
+
+ TP_fast_assign(
+ __entry->rreq = rreq->debug_id;
+ __entry->cookie = rreq->cookie_debug_id;
+ __entry->start = start;
+ __entry->len = len;
+ __entry->what = what;
+ ),
+
+ TP_printk("R=%08x %s c=%08x s=%llx %zx",
+ __entry->rreq,
+ __print_symbolic(__entry->what, netfs_read_traces),
+ __entry->cookie,
+ __entry->start, __entry->len)
+ );
+
+TRACE_EVENT(netfs_rreq,
+ TP_PROTO(struct netfs_read_request *rreq,
+ enum netfs_rreq_trace what),
+
+ TP_ARGS(rreq, what),
+
+ TP_STRUCT__entry(
+ __field(unsigned int, rreq )
+ __field(unsigned short, flags )
+ __field(enum netfs_rreq_trace, what )
+ ),
+
+ TP_fast_assign(
+ __entry->rreq = rreq->debug_id;
+ __entry->flags = rreq->flags;
+ __entry->what = what;
+ ),
+
+ TP_printk("R=%08x %s f=%02x",
+ __entry->rreq,
+ __print_symbolic(__entry->what, netfs_rreq_traces),
+ __entry->flags)
+ );
+
+TRACE_EVENT(netfs_sreq,
+ TP_PROTO(struct netfs_read_subrequest *sreq,
+ enum netfs_sreq_trace what),
+
+ TP_ARGS(sreq, what),
+
+ TP_STRUCT__entry(
+ __field(unsigned int, rreq )
+ __field(unsigned short, index )
+ __field(short, error )
+ __field(unsigned short, flags )
+ __field(enum netfs_read_source, source )
+ __field(enum netfs_sreq_trace, what )
+ __field(size_t, len )
+ __field(size_t, transferred )
+ __field(loff_t, start )
+ ),
+
+ TP_fast_assign(
+ __entry->rreq = sreq->rreq->debug_id;
+ __entry->index = sreq->debug_index;
+ __entry->error = sreq->error;
+ __entry->flags = sreq->flags;
+ __entry->source = sreq->source;
+ __entry->what = what;
+ __entry->len = sreq->len;
+ __entry->transferred = sreq->transferred;
+ __entry->start = sreq->start;
+ ),
+
+ TP_printk("R=%08x[%u] %s %s f=%02x s=%llx %zx/%zx e=%d",
+ __entry->rreq, __entry->index,
+ __print_symbolic(__entry->what, netfs_sreq_traces),
+ __print_symbolic(__entry->source, netfs_sreq_sources),
+ __entry->flags,
+ __entry->start, __entry->transferred, __entry->len,
+ __entry->error)
+ );
+
+#endif /* _TRACE_NETFS_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>

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