Hi Jaegeuk, Chao,
On 09/10/2013 08:52 AM, Jaegeuk Kim wrote:
> 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.
IMHO, just moving sbi->next_lock_num++ before mutex_lock(&sbi->fs_lock[next_lock])
can avoid unbalance issue mostly.
IMO, the case two or more threads increase sbi->next_lock_num in the same time is
really very very little. If you think it is not rigorous, change next_lock_num to
atomic one can fix it.
What's your opinion?
Regards,
Gu
>
> So, how about removing the spin_lock?
> And how about using a random number?
> Thanks,
>
> 2013-09-06 (금), 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 <chao2.yu@xxxxxxxxxxx>
>>
>> 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)
>>
>>
>>
>>
>>
>>
>
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