On fri, 1 Feb 2013 10:53:30 +0800, Liu Bo wrote:
> On Thu, Jan 31, 2013 at 05:39:03PM +0800, Miao Xie wrote:
>> This idea is from ext4. By this patch, we can make the dio write parallel,
>> and improve the performance.
>
> Interesting, AFAIK, ext4 can only do nolock dio write on some
> conditions(should be a overwrite, file size remains unchanged,
> no aligned/buffer io in flight), btrfs is ok without any conditions?
ext4 don't have extent lock, it can not avoid 2 AIO threads are at work on the same
unwritten block, so it can not use unlocked dio write for unaligned dio/aio. But btrfs
has extent lock, it can avoid this problem.
And ext4 need take write lock of ->i_data_sem, when it allocate the free space,
but in order to avoid truncation and hole punch during dio, it need take the read
lock of ->i_data_sem before it release ->i_mutex, that is if it isn't a overwrite,
deadlock will happen, so the unlocked dio of ext4 should be a overwrite. But btrfs
doesn't have such limitation.
Thanks
Miao
>
> thanks,
> liubo
>
>>
>> We needn't worry about the race between dio write and truncate, because the
>> truncate need wait untill all the dio write end.
>>
>> And we also needn't worry about the race between dio write and punch hole,
>> because we have extent lock to protect our operation.
>>
>> I ran fio to test the performance of this feature.
>>
>> == Hardware ==
>> CPU: Intel(R) Core(TM)2 Duo CPU E7500 @ 2.93GHz
>> Mem: 2GB
>> SSD: Intel X25-M 120GB (Test Partition: 60GB)
>>
>> == config file ==
>> [global]
>> ioengine=psync
>> direct=1
>> bs=4k
>> size=32G
>> runtime=60
>> directory=/mnt/btrfs/
>> filename=testfile
>> group_reporting
>> thread
>>
>> [file1]
>> numjobs=1 # 2 4
>> rw=randwrite
>>
>> == result (KBps) ==
>> write 1 2 4
>> lock 24936 24738 24726
>> nolock 24962 30866 32101
>>
>> == result (iops) ==
>> write 1 2 4
>> lock 6234 6184 6181
>> nolock 6240 7716 8025
>>
>> Signed-off-by: Miao Xie <miaox@xxxxxxxxxxxxxx>
>> ---
>> fs/btrfs/inode.c | 24 +++++++++++++-----------
>> 1 file changed, 13 insertions(+), 11 deletions(-)
>>
>> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
>> index d17a04b..091593a 100644
>> --- a/fs/btrfs/inode.c
>> +++ b/fs/btrfs/inode.c
>> @@ -6589,31 +6589,33 @@ static ssize_t btrfs_direct_IO(int rw, struct kiocb *iocb,
>> struct file *file = iocb->ki_filp;
>> struct inode *inode = file->f_mapping->host;
>> int flags = 0;
>> - bool wakeup = false;
>> + bool wakeup = true;
>> int ret;
>>
>> if (check_direct_IO(BTRFS_I(inode)->root, rw, iocb, iov,
>> offset, nr_segs))
>> return 0;
>>
>> - if (rw == READ) {
>> - atomic_inc(&inode->i_dio_count);
>> - smp_mb__after_atomic_inc();
>> - if (unlikely(test_bit(BTRFS_INODE_READDIO_NEED_LOCK,
>> - &BTRFS_I(inode)->runtime_flags))) {
>> - inode_dio_done(inode);
>> - flags = DIO_LOCKING | DIO_SKIP_HOLES;
>> - } else {
>> - wakeup = true;
>> - }
>> + atomic_inc(&inode->i_dio_count);
>> + smp_mb__after_atomic_inc();
>> + if (rw == WRITE) {
>> + mutex_unlock(&inode->i_mutex);
>> + } else if (unlikely(test_bit(BTRFS_INODE_READDIO_NEED_LOCK,
>> + &BTRFS_I(inode)->runtime_flags))) {
>> + inode_dio_done(inode);
>> + flags = DIO_LOCKING | DIO_SKIP_HOLES;
>> + wakeup = false;
>> }
>>
>> ret = __blockdev_direct_IO(rw, iocb, inode,
>> BTRFS_I(inode)->root->fs_info->fs_devices->latest_bdev,
>> iov, offset, nr_segs, btrfs_get_blocks_direct, NULL,
>> btrfs_submit_direct, flags);
>> +
>> if (wakeup)
>> inode_dio_done(inode);
>> + if (rw == WRITE)
>> + mutex_lock(&inode->i_mutex);
>> return ret;
>> }
>>
>> --
>> 1.7.11.7
>> --
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