Hi Kim,
I did some tests as you mention of using random instead of spin_lock.
The test model is as following:
eight threads race to grab one of eight locks for one thousand times,
and I used four methods to generate lock num:
1.atomic_add_return(1, &sbi->next_lock_num) % NR_GLOBAL_LOCKS;
2.spin_lock(); next_lock_num++ % NR_GLOBAL_LOCKS; spin_unlock();
3.ktime_get().tv64 % NR_GLOBAL_LOCKS;
4.get_random_bytes(&next_lock, sizeof(unsigned int));
the result indicate that:
max count of collide continuously: 4 > 3 > 2 = 1
max-min count of lock is grabbed: 4 > 3 > 2 = 1
elapsed time of generating: 3 > 2 > 4 > 1
So I think it's better to use atomic_add_return in round-robin method to
cost less time and reduce collide.
What's your opinion?
thanks
------- Original Message -------
Sender : ???<jaegeuk.kim@xxxxxxxxxxx> S5(??)/??/?????????(???)/????
Date : 九月 10, 2013 09:52 (GMT+09:00)
Title : Re: [f2fs-dev][PATCH] f2fs: optimize fs_lock for better performance
Hi,
At first, thank you for the report and please follow the email writing
rules. :)
Anyway, I agree to the below issue.
One thing that I can think of is that we don't need to use the
spin_lock, since we don't care about the exact lock number, but just
need to get any not-collided number.
So, how about removing the spin_lock?
And how about using a random number?
Thanks,
2013-09-06 (?), 09:48 +0000, Chao Yu:
> Hi Kim:
>
> I think there is a performance problem: when all sbi->fs_lock is
> holded,
>
> then all other threads may get the same next_lock value from
> sbi->next_lock_num in function mutex_lock_op,
>
> and wait to get the same lock at position fs_lock[next_lock], it
> unbalance the fs_lock usage.
>
> It may lost performance when we do the multithread test.
>
>
>
> Here is the patch to fix this problem:
>
>
>
> Signed-off-by: Yu Chao
>
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>
> old mode 100644
>
> new mode 100755
>
> index 467d42d..983bb45
>
> --- a/fs/f2fs/f2fs.h
>
> +++ b/fs/f2fs/f2fs.h
>
> @@ -371,6 +371,7 @@ struct f2fs_sb_info {
>
> struct mutex fs_lock[NR_GLOBAL_LOCKS]; /* blocking FS
> operations */
>
> struct mutex node_write; /* locking node writes
> */
>
> struct mutex writepages; /* mutex for
> writepages() */
>
> + spinlock_t spin_lock; /* lock for
> next_lock_num */
>
> unsigned char next_lock_num; /* round-robin global
> locks */
>
> int por_doing; /* recovery is doing
> or not */
>
> int on_build_free_nids; /* build_free_nids is
> doing */
>
> @@ -533,15 +534,19 @@ static inline void mutex_unlock_all(struct
> f2fs_sb_info *sbi)
>
>
>
> static inline int mutex_lock_op(struct f2fs_sb_info *sbi)
>
> {
>
> - unsigned char next_lock = sbi->next_lock_num %
> NR_GLOBAL_LOCKS;
>
> + unsigned char next_lock;
>
> int i = 0;
>
>
>
> for (; i < NR_GLOBAL_LOCKS; i++)
>
> if (mutex_trylock(&sbi->fs_lock[i]))
>
> return i;
>
>
>
> - mutex_lock(&sbi->fs_lock[next_lock]);
>
> + spin_lock(&sbi->spin_lock);
>
> + next_lock = sbi->next_lock_num % NR_GLOBAL_LOCKS;
>
> sbi->next_lock_num++;
>
> + spin_unlock(&sbi->spin_lock);
>
> +
>
> + mutex_lock(&sbi->fs_lock[next_lock]);
>
> return next_lock;
>
> }
>
>
>
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>
> old mode 100644
>
> new mode 100755
>
> index 75c7dc3..4f27596
>
> --- a/fs/f2fs/super.c
>
> +++ b/fs/f2fs/super.c
>
> @@ -657,6 +657,7 @@ static int f2fs_fill_super(struct super_block *sb,
> void *data, int silent)
>
> mutex_init(&sbi->cp_mutex);
>
> for (i = 0; i < NR_GLOBAL_LOCKS; i++)
>
> mutex_init(&sbi->fs_lock[i]);
>
> + spin_lock_init(&sbi->spin_lock);
>
> mutex_init(&sbi->node_write);
>
> sbi->por_doing = 0;
>
> spin_lock_init(&sbi->stat_lock);
>
> (END)
>
>
>
>
>
>
--
Jaegeuk Kim
Samsung?韬{.n?????%??檩??w?{.n???{饼?z鳐??骅w* jg????????G??⒏ ⒎?:+v???????? ????＂??????
