Messages in this thread | | | Date | Thu, 15 Apr 2010 10:47:57 +0200 | From | Jan Kara <> | Subject | Re: [PATCH] Fix regression in O_DIRECT|O_SYNC writes to block devices |
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On Thu 15-04-10 14:40:39, Anton Blanchard wrote: > > We are seeing a large regression in database performance on recent kernels. > The database opens a block device with O_DIRECT|O_SYNC and a number of threads > write to different regions of the file at the same time. > > A simple test case is below. I haven't defined DEVICE to anything since getting > it wrong will destroy your data :) On an 3 disk LVM with a 64k chunk size we > see about 17MB/sec and only a few threads in IO wait: > > procs -----io---- -system-- -----cpu------ > r b bi bo in cs us sy id wa st > 0 3 0 16170 656 2259 0 0 86 14 0 > 0 2 0 16704 695 2408 0 0 92 8 0 > 0 2 0 17308 744 2653 0 0 86 14 0 > 0 2 0 17933 759 2777 0 0 89 10 0 > > Most threads are blocking in vfs_fsync_range, which has: > > mutex_lock(&mapping->host->i_mutex); > err = fop->fsync(file, dentry, datasync); > if (!ret) > ret = err; > mutex_unlock(&mapping->host->i_mutex); ... Just a few style nitpicks:
> Index: linux-2.6/fs/block_dev.c > =================================================================== > --- linux-2.6.orig/fs/block_dev.c 2010-04-14 12:55:50.000000000 +1000 > +++ linux-2.6/fs/block_dev.c 2010-04-14 13:17:45.000000000 +1000 > @@ -406,16 +406,24 @@ static loff_t block_llseek(struct file * > > int blkdev_fsync(struct file *filp, struct dentry *dentry, int datasync) > { > - struct block_device *bdev = I_BDEV(filp->f_mapping->host); > + struct inode *bd_inode = filp->f_mapping->host; > + struct block_device *bdev = I_BDEV(bd_inode); > int error; > Could you please add a comment here? Like "There is no need to protect syncing of the block device by i_mutex and it unnecessarily serializes workloads with several O_SYNC writers to the block device"
> + mutex_unlock(&bd_inode->i_mutex); > + > error = sync_blockdev(bdev); > - if (error) > + if (error) { > + mutex_lock(&bd_inode->i_mutex); > return error; Usually, "goto out" is preferred instead of the above.
> + } > > error = blkdev_issue_flush(bdev, NULL); > if (error == -EOPNOTSUPP) > error = 0; > + And define out: here.
> + mutex_lock(&bd_inode->i_mutex); > + > return error; > } > EXPORT_SYMBOL(blkdev_fsync);
Honza -- Jan Kara <jack@suse.cz> SUSE Labs, CR
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