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Date: Wed, 6 Aug 2008 15:23:54 -0400
From: Josef Bacik <jbacik@...hat.com>
To: Josef Bacik <jbacik@...hat.com>
Cc: linux-kernel@...r.kernel.org, rwheeler@...hat.com,
tglx@...utronix.de, linux-fsdevel@...r.kernel.org,
chris.mason@...cle.com, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 2/2] improve ext3 fsync batching
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@...hat.com>
>
> 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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