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![Dave Chinner](/assets/img/avatar_default.png)
Michael L Semon reported that generic/069 runtime increased on v5 superblocks by 100% compared to v4 superblocks. his perf-based analysis pointed directly at the timestamp updates being done by the write path in this workload. The append writers are doing 4-byte writes, so there are lots of timestamp updates occurring. The thing is, they aren't being triggered by timestamp changes - they are being triggered by the inode change counter needing to be updated. That is, every write(2) system call needs to bump the inode version count, and it does that through the timestamp update mechanism. Hence for v5 filesystems, test generic/069 is running 3 orders of magnitude more timestmap update transactions on v5 filesystems due to the fact it does a huge number of *4 byte* write(2) calls. This isn't a real world scenario we really need to address - anyone doing such sequential IO should be using fwrite(3), not write(2). i.e. fwrite(3) buffers the writes in userspace to minimise the number of write(2) syscalls, and the problem goes away. However, there is a small change we can make to improve the situation - removing the expensive lock operation on the change counter update. All inode version counter changes in XFS occur under the ip->i_ilock during a transaction, and therefore we don't actually need the spin lock that provides exclusive access to it through inc_inode_iversion(). Hence avoid the lock and just open code the increment ourselves when logging the inode. Reported-by: Michael L. Semon <mlsemon35@gmail.com> Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Ben Myers <bpm@sgi.com>
137 lines
4 KiB
C
137 lines
4 KiB
C
/*
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* Copyright (c) 2000,2005 Silicon Graphics, Inc.
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* All Rights Reserved.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it would be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include "xfs.h"
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#include "xfs_fs.h"
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#include "xfs_shared.h"
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#include "xfs_format.h"
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#include "xfs_log_format.h"
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#include "xfs_trans_resv.h"
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#include "xfs_sb.h"
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#include "xfs_ag.h"
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#include "xfs_mount.h"
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#include "xfs_inode.h"
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#include "xfs_trans.h"
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#include "xfs_trans_priv.h"
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#include "xfs_inode_item.h"
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#include "xfs_trace.h"
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/*
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* Add a locked inode to the transaction.
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*
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* The inode must be locked, and it cannot be associated with any transaction.
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* If lock_flags is non-zero the inode will be unlocked on transaction commit.
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*/
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void
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xfs_trans_ijoin(
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struct xfs_trans *tp,
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struct xfs_inode *ip,
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uint lock_flags)
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{
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xfs_inode_log_item_t *iip;
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ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
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if (ip->i_itemp == NULL)
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xfs_inode_item_init(ip, ip->i_mount);
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iip = ip->i_itemp;
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ASSERT(iip->ili_lock_flags == 0);
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iip->ili_lock_flags = lock_flags;
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/*
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* Get a log_item_desc to point at the new item.
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*/
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xfs_trans_add_item(tp, &iip->ili_item);
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}
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/*
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* Transactional inode timestamp update. Requires the inode to be locked and
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* joined to the transaction supplied. Relies on the transaction subsystem to
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* track dirty state and update/writeback the inode accordingly.
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*/
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void
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xfs_trans_ichgtime(
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struct xfs_trans *tp,
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struct xfs_inode *ip,
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int flags)
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{
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struct inode *inode = VFS_I(ip);
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timespec_t tv;
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ASSERT(tp);
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ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
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tv = current_fs_time(inode->i_sb);
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if ((flags & XFS_ICHGTIME_MOD) &&
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!timespec_equal(&inode->i_mtime, &tv)) {
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inode->i_mtime = tv;
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ip->i_d.di_mtime.t_sec = tv.tv_sec;
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ip->i_d.di_mtime.t_nsec = tv.tv_nsec;
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}
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if ((flags & XFS_ICHGTIME_CHG) &&
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!timespec_equal(&inode->i_ctime, &tv)) {
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inode->i_ctime = tv;
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ip->i_d.di_ctime.t_sec = tv.tv_sec;
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ip->i_d.di_ctime.t_nsec = tv.tv_nsec;
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}
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}
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/*
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* This is called to mark the fields indicated in fieldmask as needing
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* to be logged when the transaction is committed. The inode must
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* already be associated with the given transaction.
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*
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* The values for fieldmask are defined in xfs_inode_item.h. We always
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* log all of the core inode if any of it has changed, and we always log
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* all of the inline data/extents/b-tree root if any of them has changed.
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*/
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void
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xfs_trans_log_inode(
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xfs_trans_t *tp,
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xfs_inode_t *ip,
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uint flags)
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{
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ASSERT(ip->i_itemp != NULL);
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ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
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/*
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* First time we log the inode in a transaction, bump the inode change
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* counter if it is configured for this to occur. We don't use
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* inode_inc_version() because there is no need for extra locking around
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* i_version as we already hold the inode locked exclusively for
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* metadata modification.
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*/
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if (!(ip->i_itemp->ili_item.li_desc->lid_flags & XFS_LID_DIRTY) &&
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IS_I_VERSION(VFS_I(ip))) {
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ip->i_d.di_changecount = ++VFS_I(ip)->i_version;
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flags |= XFS_ILOG_CORE;
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}
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tp->t_flags |= XFS_TRANS_DIRTY;
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ip->i_itemp->ili_item.li_desc->lid_flags |= XFS_LID_DIRTY;
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/*
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* Always OR in the bits from the ili_last_fields field.
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* This is to coordinate with the xfs_iflush() and xfs_iflush_done()
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* routines in the eventual clearing of the ili_fields bits.
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* See the big comment in xfs_iflush() for an explanation of
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* this coordination mechanism.
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*/
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flags |= ip->i_itemp->ili_last_fields;
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ip->i_itemp->ili_fields |= flags;
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}
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