In function xfs_file_aio_read, will request XFS_IOLOCK_SHARED lock for both direct IO and buffered IO:
STATIC ssize_t
xfs_file_aio_read(
struct kiocb *iocb,
const struct iovec *iovp,
unsigned long nr_segs,
loff_t pos)
{
...
xfs_rw_ilock(ip, XFS_IOLOCK_SHARED);
so write will prevent read in XFS.
However, in function generic_file_aio_read for ext3, will not lock inode->i_mutex, so write will not prevent read in ext3.
I think this maybe the reason of poor performance for XFS. I do not know if this is a bug, or design flaws of XFS.
Brian and Eric,
Thanks very much for your replay.
I changed partition start position with 256K, but the performance is still poor, no change.
# fdisk -ul /dev/sdb
Device Boot Start End Blocks Id System
/dev/sdb1 512 2929356359 1464677924 83 Linux
I checked the XFS’s code, I agree that XFS_IOLOCK_EXCL lock maybe the reason:
STATIC ssize_t
xfs_file_buffered_aio_write(
struct kiocb *iocb,
const struct iovec *iovp,
unsigned long nr_segs,
loff_t pos,
size_t ocount)
{
struct file *file = iocb->ki_filp;
struct address_space *mapping = file->f_mapping;
struct inode *inode = mapping->host;
struct xfs_inode *ip = XFS_I(inode);
ssize_t ret;
int enospc = 0;
int iolock = XFS_IOLOCK_EXCL;
size_t count = ocount;
xfs_rw_ilock(ip, iolock);
ret = xfs_file_aio_write_checks(file, &pos, &count, &iolock);
if (ret)
However，I found that EXT3 also have mutex when with buffered IO:
ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
unsigned long nr_segs, loff_t pos)
{
struct file *file = iocb->ki_filp;
struct inode *inode = file->f_mapping->host;
ssize_t ret;
BUG_ON(iocb->ki_pos != pos);
sb_start_write(inode->i_sb);
mutex_lock(&inode->i_mutex);
ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
mutex_unlock(&inode->i_mutex);
I still don’t understand why ext3 does not have this problem with buffered IO.
On 2/11/15 1:39 AM, yy wrote: <snip> (In addition to Brian's questions): > XFS format parametes: > > #mkfs.xfs -d su=256k,sw=5 /dev/sdb1 > > #cat /proc/mounts > > /dev/sdb1 /data1 xfs rw,noatime,attr2,delaylog,nobarrier,logbsize=256k,sunit=512,swidth=2560,noquota 0 0 > > #fdisk -ul > Device Boot Start End Blocks Id System > /dev/sdb1 128 2929356359 1464678116 83 Linux so 128*512 = 64k; your partition doesn't start on a 256k stripe unit boundary, right? Shouldn't it do so? -Eric
_______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
