Re: [PATCH 2/2] improve ext3 fsync batching

[Josef Bacik]

On Wed, Aug 06, 2008 at 03:15:36PM -0400, Josef Bacik wrote:
> Hello,
> 
> Fsync batching in ext3 is somewhat flawed when it comes to disks that are very
> fast.  Now we do an unconditional sleep for 1 second, which is great on slow
> disks like SATA and such, but on fast disks this means just sitting around and
> waiting for nothing.  This patch measures the time it takes to commit a
> transaction to the disk, and sleeps based on the speed of the underlying disk.
> Using the following fs_mark command to test the speeds
> 
> ./fs_mark -d /mnt/ext3-test -s 4096 -n 2000 -D 64 -t 2
> 
> I got the following results (with write cacheing turned off)
> 
> type	threads		with patch	without patch
> sata	2		26.4		27.8
> sata	4		44.6		44.4
> sata	8		70.4		72.8
> sata	16		75.2		89.6
> sata	32		92.7		96.0
> ram	1		2399.1		2398.8
> ram	2		257.3		3603.0
> ram	4		395.6		4827.9
> ram	8		659.0		4721.1
> ram	16		1326.4		4373.3
> ram	32		1964.2		3816.3
>

Err sorry about that, the with patch and without patch colums should be
reversed.  Thanks,

Josef
 
> I used a ramdisk to emulate a "fast" disk since I don't happen to have a
> clariion sitting around.  I didn't test single thread in the sata case as it
> should be relatively the same between the two.  Thanks,
> 
> Signed-off-by: Josef Bacik <jbacik@xxxxxxxxxx>
> 
> Index: linux-2.6/fs/jbd/commit.c
> ===================================================================
> --- linux-2.6.orig/fs/jbd/commit.c
> +++ linux-2.6/fs/jbd/commit.c
> @@ -288,6 +288,8 @@ void journal_commit_transaction(journal_
>  	int flags;
>  	int err;
>  	unsigned long blocknr;
> +	ktime_t start_time;
> +	u64 commit_time;
>  	char *tagp = NULL;
>  	journal_header_t *header;
>  	journal_block_tag_t *tag = NULL;
> @@ -400,6 +402,7 @@ void journal_commit_transaction(journal_
>  	commit_transaction->t_state = T_FLUSH;
>  	journal->j_committing_transaction = commit_transaction;
>  	journal->j_running_transaction = NULL;
> +	start_time = ktime_get();
>  	commit_transaction->t_log_start = journal->j_head;
>  	wake_up(&journal->j_wait_transaction_locked);
>  	spin_unlock(&journal->j_state_lock);
> @@ -873,6 +876,18 @@ restart_loop:
>  	J_ASSERT(commit_transaction == journal->j_committing_transaction);
>  	journal->j_commit_sequence = commit_transaction->t_tid;
>  	journal->j_committing_transaction = NULL;
> +	commit_time = ktime_to_ns(ktime_sub(ktime_get(), start_time));
> +
> +	/*
> +	 * weight the commit time higher than the average time so we don't
> +	 * react too strongly to vast changes in commit time
> +	 */
> +	if (likely(journal->j_average_commit_time))
> +		journal->j_average_commit_time = (commit_time*3 +
> +				journal->j_average_commit_time) / 4;
> +	else
> +		journal->j_average_commit_time = commit_time;
> +
>  	spin_unlock(&journal->j_state_lock);
>  
>  	if (commit_transaction->t_checkpoint_list == NULL &&
> Index: linux-2.6/fs/jbd/transaction.c
> ===================================================================
> --- linux-2.6.orig/fs/jbd/transaction.c
> +++ linux-2.6/fs/jbd/transaction.c
> @@ -25,6 +25,7 @@
>  #include <linux/timer.h>
>  #include <linux/mm.h>
>  #include <linux/highmem.h>
> +#include <linux/hrtimer.h>
>  
>  static void __journal_temp_unlink_buffer(struct journal_head *jh);
>  
> @@ -49,6 +50,7 @@ get_transaction(journal_t *journal, tran
>  {
>  	transaction->t_journal = journal;
>  	transaction->t_state = T_RUNNING;
> +	transaction->t_start_time = ktime_get();
>  	transaction->t_tid = journal->j_transaction_sequence++;
>  	transaction->t_expires = jiffies + journal->j_commit_interval;
>  	spin_lock_init(&transaction->t_handle_lock);
> @@ -1361,7 +1363,7 @@ int journal_stop(handle_t *handle)
>  {
>  	transaction_t *transaction = handle->h_transaction;
>  	journal_t *journal = transaction->t_journal;
> -	int old_handle_count, err;
> +	int err;
>  	pid_t pid;
>  
>  	J_ASSERT(journal_current_handle() == handle);
> @@ -1397,11 +1399,18 @@ int journal_stop(handle_t *handle)
>  	 */
>  	pid = current->pid;
>  	if (handle->h_sync && journal->j_last_sync_writer != pid) {
> +		u64 commit_time, trans_time;
> +
>  		journal->j_last_sync_writer = pid;
> -		do {
> -			old_handle_count = transaction->t_handle_count;
> -			schedule_timeout_uninterruptible(1);
> -		} while (old_handle_count != transaction->t_handle_count);
> +
> +		spin_lock(&journal->j_state_lock);
> +		commit_time = journal->j_average_commit_time;
> +		spin_unlock(&journal->j_state_lock);
> +
> +		trans_time = ktime_to_ns(ktime_sub(ktime_get(),
> +						   transaction->t_start_time));
> +		if (trans_time < commit_time)
> +			hrtimer_sleep_ns(commit_time, 1);
>  	}
>  
>  	current->journal_info = NULL;
> Index: linux-2.6/include/linux/jbd.h
> ===================================================================
> --- linux-2.6.orig/include/linux/jbd.h
> +++ linux-2.6/include/linux/jbd.h
> @@ -543,6 +543,11 @@ struct transaction_s
>  	unsigned long		t_expires;
>  
>  	/*
> +	 * When this transaction started, in nanoseconds [no locking]
> +	 */
> +	ktime_t			t_start_time;
> +
> +	/*
>  	 * How many handles used this transaction? [t_handle_lock]
>  	 */
>  	int t_handle_count;
> @@ -800,6 +805,8 @@ struct journal_s
>  
>  	pid_t			j_last_sync_writer;
>  
> +	u64			j_average_commit_time;
> +
>  	/*
>  	 * An opaque pointer to fs-private information.  ext3 puts its
>  	 * superblock pointer here
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