On Thu, Sep 12, 2013 at 04:08:24PM +0800, Qu Wenruo wrote:
> The original btrfs_workers uses the fs_info->thread_pool_size as the
> max_active, and the previous patches followed this way.
>
> But the kernel workqueue has the default value(0) for workqueue,
> and workqueue itself has some threshold mechanism to prevent creating
> too many threads, so we should use the default value.
>
> Since the thread_pool_size algorithm is not used, related codes should
> also be changed.
Ohh, I should have seen this mail first before commenting 'max_active'.
I think that some tuning work should be done on this part, according to
my tests, setting max_active=0 will create ~258 worker helpers
(kworker/uX:X if you set WQ_UNBOUND), this may cause too many context
switches which will have an impact on performance in some cases.
-liubo
>
> Signed-off-by: Qu Wenruo <quwen...@cn.fujitsu.com>
> ---
> fs/btrfs/disk-io.c | 12 +++++++-----
> fs/btrfs/super.c | 3 +--
> 2 files changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index a61e1fe..0446d27 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -750,9 +750,11 @@ int btrfs_bio_wq_end_io(struct btrfs_fs_info *info,
> struct bio *bio,
>
> unsigned long btrfs_async_submit_limit(struct btrfs_fs_info *info)
> {
> - unsigned long limit = min_t(unsigned long,
> - info->thread_pool_size,
> - info->fs_devices->open_devices);
> + unsigned long limit;
> + limit = info->thread_pool_size ?
> + min_t(unsigned long, info->thread_pool_size,
> + info->fs_devices->open_devices) :
> + info->fs_devices->open_devices;
> return 256 * limit;
> }
>
> @@ -2191,8 +2193,8 @@ int open_ctree(struct super_block *sb,
> INIT_RADIX_TREE(&fs_info->reada_tree, GFP_NOFS & ~__GFP_WAIT);
> spin_lock_init(&fs_info->reada_lock);
>
> - fs_info->thread_pool_size = min_t(unsigned long,
> - num_online_cpus() + 2, 8);
> + /* use the default value of kernel workqueue */
> + fs_info->thread_pool_size = 0;
>
> INIT_LIST_HEAD(&fs_info->ordered_roots);
> spin_lock_init(&fs_info->ordered_root_lock);
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 63e653c..ccf412f 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -898,8 +898,7 @@ static int btrfs_show_options(struct seq_file *seq,
> struct dentry *dentry)
> if (info->alloc_start != 0)
> seq_printf(seq, ",alloc_start=%llu",
> (unsigned long long)info->alloc_start);
> - if (info->thread_pool_size != min_t(unsigned long,
> - num_online_cpus() + 2, 8))
> + if (info->thread_pool_size)
> seq_printf(seq, ",thread_pool=%d", info->thread_pool_size);
> if (btrfs_test_opt(root, COMPRESS)) {
> if (info->compress_type == BTRFS_COMPRESS_ZLIB)
> --
> 1.8.4
>
> --
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