[PATCH v3 0/2] btrfs: Expose BTRFS commit stats through sysfs

[PATCH v3 0/2] btrfs: Expose BTRFS commit stats through sysfs

[Ioannis Angelakopoulos]

With this patch series we add the capability to BTRFS to expose some
commit stats through sysfs that might be useful for performance monitoring
and debugging purposes.

Specifically, through SYSFS we expose the following data:
  1) A counter for the commits that occurred so far.
  2) The duration in ms of the last commit.
  3) The maximum commit duration in ms seen so far.
  4) The total duration in ms of the commits seen so far.

The user also has the capability to reset the maximum commit duration
back to zero, again through SYSFS.

Changes from v2:

1) Only the maximum duration can now be zeroed out through sysfs to
prevent loss of data if multiple threads try to reset the commit stats
simultaneously
2) Removed the lock that protected the concurrent resetting and updating
of the commit stats, since only the maximum commit duration can be
cleared out now (any races can be ignored for this stat).
3) Added div_u64 when converting from ns to ms, to also support 32-bit
4) Made the output from sysfs easier to use with "grep"

Changes from v1:

1) Edited out unnecessary comments
2) Made the memory allocation of "btrfs_commit_stats" under "fs_info" in
fs/btrfs/ctree.h static instead of dynamic
3) Transferred the conversion from ns to ms at the point where commit
stats get printed in sysfs, for better precision
4) Changed the lock that protects the update of the commit stats from
"trans_lock" to "super_lock"
5) Changed the printing of the commits stats in sysfs to conform with
the sysfs output

Ioannis Angelakopoulos (2):
  btrfs: Add the capability of getting commit stats in BTRFS
  btrfs: Expose the BTRFS commit stats through sysfs

 fs/btrfs/ctree.h       | 14 +++++++++++++
 fs/btrfs/sysfs.c       | 45 ++++++++++++++++++++++++++++++++++++++++++
 fs/btrfs/transaction.c | 22 +++++++++++++++++++++
 3 files changed, 81 insertions(+)

-- 
2.30.2

[PATCH v3 1/2] btrfs: Add the capability of getting commit stats in BTRFS

[Ioannis Angelakopoulos]

First we add  "struct btrfs_commit_stats" data structure under "fs_info"
in fs/btrfs/ctree.h to store the commit stats for BTRFS that will be
exposed through sysfs.

The stats exposed are: 1) The number of commits so far, 2) The duration of
the last commit in ms, 3) The maximum commit duration seen so far in ms
and 4) The total duration for all commits so far in ms.

The update of the commit stats occurs after the commit thread has gone
through all the logic that checks if there is another thread committing
at the same time. This means that we only account for actual commit work
in the commit stats we report and not the time the thread spends waiting
until it is ready to do the commit work.

Signed-off-by: Ioannis Angelakopoulos <iangelak@fb.com>
---
 fs/btrfs/ctree.h       | 14 ++++++++++++++
 fs/btrfs/transaction.c | 22 ++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 1347c92234a5..2bd4a53c0046 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -667,6 +667,18 @@ enum btrfs_exclusive_operation {
 	BTRFS_EXCLOP_SWAP_ACTIVATE,
 };
 
+/* Storing data about btrfs commits. The data are accessible over sysfs */
+struct btrfs_commit_stats {
+	/* Total number of commits */
+	u64 commit_counter;
+	/* The maximum commit duration so far*/
+	u64 max_commit_dur;
+	/* The last commit duration */
+	u64 last_commit_dur;
+	/* The total commit duration */
+	u64 total_commit_dur;
+};
+
 struct btrfs_fs_info {
 	u8 chunk_tree_uuid[BTRFS_UUID_SIZE];
 	unsigned long flags;
@@ -1076,6 +1088,8 @@ struct btrfs_fs_info {
 	spinlock_t zone_active_bgs_lock;
 	struct list_head zone_active_bgs;
 
+	struct btrfs_commit_stats commit_stats;
+
 #ifdef CONFIG_BTRFS_FS_REF_VERIFY
 	spinlock_t ref_verify_lock;
 	struct rb_root block_tree;
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 06c0a958d114..5b9451b3b005 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -10,6 +10,7 @@
 #include <linux/pagemap.h>
 #include <linux/blkdev.h>
 #include <linux/uuid.h>
+#include <linux/timekeeping.h>
 #include "misc.h"
 #include "ctree.h"
 #include "disk-io.h"
@@ -2084,12 +2085,23 @@ static void add_pending_snapshot(struct btrfs_trans_handle *trans)
 	list_add(&trans->pending_snapshot->list, &cur_trans->pending_snapshots);
 }
 
+static void update_commit_stats(struct btrfs_fs_info *fs_info, ktime_t interval)
+{
+	fs_info->commit_stats.commit_counter++;
+	fs_info->commit_stats.last_commit_dur = interval;
+	fs_info->commit_stats.max_commit_dur = max_t(u64,
+				fs_info->commit_stats.max_commit_dur, interval);
+	fs_info->commit_stats.total_commit_dur += interval;
+}
+
 int btrfs_commit_transaction(struct btrfs_trans_handle *trans)
 {
 	struct btrfs_fs_info *fs_info = trans->fs_info;
 	struct btrfs_transaction *cur_trans = trans->transaction;
 	struct btrfs_transaction *prev_trans = NULL;
 	int ret;
+	ktime_t start_time;
+	ktime_t interval;
 
 	ASSERT(refcount_read(&trans->use_count) == 1);
 
@@ -2214,6 +2226,12 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans)
 		}
 	}
 
+	/*
+	 * Get the time spent on the work done by the commit thread and not
+	 * the time spent waiting on a previous commit
+	 */
+	start_time = ktime_get_ns();
+
 	extwriter_counter_dec(cur_trans, trans->type);
 
 	ret = btrfs_start_delalloc_flush(fs_info);
@@ -2455,6 +2473,8 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans)
 
 	trace_btrfs_transaction_commit(fs_info);
 
+	interval = ktime_get_ns() - start_time;
+
 	btrfs_scrub_continue(fs_info);
 
 	if (current->journal_info == trans)
@@ -2462,6 +2482,8 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans)
 
 	kmem_cache_free(btrfs_trans_handle_cachep, trans);
 
+	update_commit_stats(fs_info, interval);
+
 	return ret;
 
 unlock_reloc:
-- 
2.30.2

[PATCH v3 2/2] btrfs: Expose the BTRFS commit stats through sysfs

[Ioannis Angelakopoulos]

Create a new sysfs entry named "commit_stats" under /sys/fs/btrfs/<UUID>/
for each mounted BTRFS filesystem. The entry exposes: 1) The number of
commits so far, 2) The duration of the last commit in ms, 3) The maximum
commit duration seen so far in ms and 4) The total duration for all commits
so far in ms.

The function "btrfs_commit_stats_show" in fs/btrfs/sysfs.c is responsible
for exposing the stats to user space.

The function "btrfs_commit_stats_store" in fs/btrfs/sysfs.c is responsible
for resetting the maximum commit duration to zero. This benefits
applications that want to sample the maximum commit duration over a long
time period. Only the maximum commit duration is reset to zero in order to
avoid loss of data if multiple threads are trying to reset the commit stats
data at the same time.

Signed-off-by: Ioannis Angelakopoulos <iangelak@fb.com>
---
 fs/btrfs/sysfs.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index db3736de14a5..0e13daa1a466 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -10,6 +10,7 @@
 #include <linux/completion.h>
 #include <linux/bug.h>
 #include <crypto/hash.h>
+#include <linux/math64.h>
 
 #include "ctree.h"
 #include "discard.h"
@@ -991,6 +992,49 @@ static ssize_t btrfs_sectorsize_show(struct kobject *kobj,
 
 BTRFS_ATTR(, sectorsize, btrfs_sectorsize_show);
 
+static ssize_t btrfs_commit_stats_show(struct kobject *kobj,
+				struct kobj_attribute *a, char *buf)
+{
+	struct btrfs_fs_info *fs_info = to_fs_info(kobj);
+
+	return sysfs_emit(buf,
+		"commits %llu\n"
+		"last_commit_dur_ms %llu\n"
+		"max_commit_dur_ms %llu\n"
+		"total_commit_dur_ms %llu\n",
+		fs_info->commit_stats.commit_counter,
+		div_u64(fs_info->commit_stats.last_commit_dur / NSEC_PER_MSEC),
+		div_u64(fs_info->commit_stats.max_commit_dur / NSEC_PER_MSEC),
+		div_u64(fs_info->commit_stats.total_commit_dur / NSEC_PER_MSEC));
+}
+
+static ssize_t btrfs_commit_stats_store(struct kobject *kobj,
+						struct kobj_attribute *a,
+						const char *buf, size_t len)
+{
+	struct btrfs_fs_info *fs_info = to_fs_info(kobj);
+	unsigned long val;
+	int ret;
+
+	if (!fs_info)
+		return -EPERM;
+
+	if (!capable(CAP_SYS_RESOURCE))
+		return -EPERM;
+
+	ret = kstrtoul(buf, 10, &val);
+	if (ret)
+		return ret;
+	if (val)
+		return -EINVAL;
+
+	fs_info->commit_stats.max_commit_dur = 0;
+
+	return len;
+}
+BTRFS_ATTR_RW(, commit_stats, btrfs_commit_stats_show,
+			  btrfs_commit_stats_store);
+
 static ssize_t btrfs_clone_alignment_show(struct kobject *kobj,
 				struct kobj_attribute *a, char *buf)
 {
@@ -1230,6 +1274,7 @@ static const struct attribute *btrfs_attrs[] = {
 	BTRFS_ATTR_PTR(, generation),
 	BTRFS_ATTR_PTR(, read_policy),
 	BTRFS_ATTR_PTR(, bg_reclaim_threshold),
+	BTRFS_ATTR_PTR(, commit_stats),
 	NULL,
 };
 
-- 
2.30.2

Re: [PATCH v3 2/2] btrfs: Expose the BTRFS commit stats through sysfs

[kernel test robot]

Hi Ioannis,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on v5.19-rc3]
[also build test ERROR on linus/master]
[cannot apply to kdave/for-next next-20220621]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/intel-lab-lkp/linux/commits/Ioannis-Angelakopoulos/btrfs-Expose-BTRFS-commit-stats-through-sysfs/20220622-055620
base:    a111daf0c53ae91e71fd2bfe7497862d14132e3e
config: hexagon-randconfig-r045-20220622 (https://download.01.org/0day-ci/archive/20220622/202206221417.F0FRQcFP-lkp@intel.com/config)
compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project 8b8d126598ce7bd5243da7f94f69fa1104288bee)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/506de693b0d08cfdf4eca94dc0528e9f46071c6e
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Ioannis-Angelakopoulos/btrfs-Expose-BTRFS-commit-stats-through-sysfs/20220622-055620
        git checkout 506de693b0d08cfdf4eca94dc0528e9f46071c6e
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=hexagon SHELL=/bin/bash fs/btrfs/

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

>> fs/btrfs/sysfs.c:886:64: error: too few arguments to function call, expected 2, have 1
                   div_u64(fs_info->commit_stats.last_commit_dur / NSEC_PER_MSEC),
                   ~~~~~~~                                                      ^
   include/linux/math64.h:125:19: note: 'div_u64' declared here
   static inline u64 div_u64(u64 dividend, u32 divisor)
                     ^
   fs/btrfs/sysfs.c:887:63: error: too few arguments to function call, expected 2, have 1
                   div_u64(fs_info->commit_stats.max_commit_dur / NSEC_PER_MSEC),
                   ~~~~~~~                                                     ^
   include/linux/math64.h:125:19: note: 'div_u64' declared here
   static inline u64 div_u64(u64 dividend, u32 divisor)
                     ^
   fs/btrfs/sysfs.c:888:65: error: too few arguments to function call, expected 2, have 1
                   div_u64(fs_info->commit_stats.total_commit_dur / NSEC_PER_MSEC));
                   ~~~~~~~                                                       ^
   include/linux/math64.h:125:19: note: 'div_u64' declared here
   static inline u64 div_u64(u64 dividend, u32 divisor)
                     ^
   3 errors generated.


vim +886 fs/btrfs/sysfs.c

   874	
   875	static ssize_t btrfs_commit_stats_show(struct kobject *kobj,
   876					struct kobj_attribute *a, char *buf)
   877	{
   878		struct btrfs_fs_info *fs_info = to_fs_info(kobj);
   879	
   880		return sysfs_emit(buf,
   881			"commits %llu\n"
   882			"last_commit_dur_ms %llu\n"
   883			"max_commit_dur_ms %llu\n"
   884			"total_commit_dur_ms %llu\n",
   885			fs_info->commit_stats.commit_counter,
 > 886			div_u64(fs_info->commit_stats.last_commit_dur / NSEC_PER_MSEC),
   887			div_u64(fs_info->commit_stats.max_commit_dur / NSEC_PER_MSEC),
   888			div_u64(fs_info->commit_stats.total_commit_dur / NSEC_PER_MSEC));
   889	}
   890	

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp