| Message ID | 162250083819.490289.18171121927859927558.stgit@locust (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | xfs: various unit conversion | expand |
On Mon, May 31, 2021 at 03:40:38PM -0700, Darrick J. Wong wrote: > From: Darrick J. Wong <djwong@kernel.org> > > Remove the unnecessary convenience variable. > > Signed-off-by: Darrick J. Wong <djwong@kernel.org> > --- > fs/xfs/xfs_inode.c | 25 +++++++++++-------------- > 1 file changed, 11 insertions(+), 14 deletions(-) > > > diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c > index e4c2da4566f1..1e28997c6f78 100644 > --- a/fs/xfs/xfs_inode.c > +++ b/fs/xfs/xfs_inode.c > @@ -689,47 +689,44 @@ xfs_inode_inherit_flags( > struct xfs_inode *ip, > const struct xfs_inode *pip) > { > - unsigned int di_flags = 0; > xfs_failaddr_t failaddr; > umode_t mode = VFS_I(ip)->i_mode; > > if (S_ISDIR(mode)) { > if (pip->i_diflags & XFS_DIFLAG_RTINHERIT) > - di_flags |= XFS_DIFLAG_RTINHERIT; > + ip->i_diflags |= XFS_DIFLAG_RTINHERIT; > if (pip->i_diflags & XFS_DIFLAG_EXTSZINHERIT) { > - di_flags |= XFS_DIFLAG_EXTSZINHERIT; > + ip->i_diflags |= XFS_DIFLAG_EXTSZINHERIT; > ip->i_extsize = pip->i_extsize; > } Hmmmm. IIRC, these functions were originally written this way because the compiler generated much better code using a local variable than when writing directly to the ip->i_d.di_flags. Is this still true now? I think it's worth checking, because we have changed the structure of the xfs_inode (removed the i_d structure) so maybe this isn't a concern anymore? Cheers, Dave.
On Tue, Jun 01, 2021 at 09:33:15AM +1000, Dave Chinner wrote: > On Mon, May 31, 2021 at 03:40:38PM -0700, Darrick J. Wong wrote: > > From: Darrick J. Wong <djwong@kernel.org> > > > > Remove the unnecessary convenience variable. > > > > Signed-off-by: Darrick J. Wong <djwong@kernel.org> > > --- > > fs/xfs/xfs_inode.c | 25 +++++++++++-------------- > > 1 file changed, 11 insertions(+), 14 deletions(-) > > > > > > diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c > > index e4c2da4566f1..1e28997c6f78 100644 > > --- a/fs/xfs/xfs_inode.c > > +++ b/fs/xfs/xfs_inode.c > > @@ -689,47 +689,44 @@ xfs_inode_inherit_flags( > > struct xfs_inode *ip, > > const struct xfs_inode *pip) > > { > > - unsigned int di_flags = 0; > > xfs_failaddr_t failaddr; > > umode_t mode = VFS_I(ip)->i_mode; > > > > if (S_ISDIR(mode)) { > > if (pip->i_diflags & XFS_DIFLAG_RTINHERIT) > > - di_flags |= XFS_DIFLAG_RTINHERIT; > > + ip->i_diflags |= XFS_DIFLAG_RTINHERIT; > > if (pip->i_diflags & XFS_DIFLAG_EXTSZINHERIT) { > > - di_flags |= XFS_DIFLAG_EXTSZINHERIT; > > + ip->i_diflags |= XFS_DIFLAG_EXTSZINHERIT; > > ip->i_extsize = pip->i_extsize; > > } > > Hmmmm. > > IIRC, these functions were originally written this way because the > compiler generated much better code using a local variable than when > writing directly to the ip->i_d.di_flags. Is this still true now? I did a quick look into the generated asm code, and although my asm is a bit rusty, I don't see that much difference between the two versions, at least not to describe it as much better code. The following is a snippet of the code with and without the patch, first line is just as a reference guide from where the ASM starts. Most of the other occurrences using di_flags variable are similar if not the same: Without patch applied: } else if (S_ISREG(mode)) { 92473: 66 81 f9 00 80 cmp $0x8000,%cx 92478: 0f 84 59 01 00 00 je 925d7 <xfs_dir_ialloc+0x797> 9248e: 41 8b b5 0c 01 00 00 mov 0x10c(%r13),%esi 92485: 31 c9 xor %ecx,%ecx 92487: a8 40 test $0x40,%al 92489: 74 15 je 924a0 <xfs_dir_ialloc+0x660> 9248b: 44 8b 1d 00 00 00 00 mov 0x0(%rip),%r11d # 92492 <xfs_dir_ialloc+0x652> 92492: 41 89 c8 mov %ecx,%r8d 92495: 41 83 c8 40 or $0x40,%r8d 92499: 45 85 db test %r11d,%r11d 9249c: 41 0f 45 c8 cmovne %r8d,%ecx 924a0: a8 80 test $0x80,%al With patch applied: } else if (S_ISREG(mode)) { 92483: 66 81 fe 00 80 cmp $0x8000,%si 92488: 0f 84 94 01 00 00 je 92622 <xfs_dir_ialloc+0x7e2> 9248e: 41 8b b5 0c 01 00 00 mov 0x10c(%r13),%esi 92495: a8 40 test $0x40,%al 92497: 74 20 je 924b9 <xfs_dir_ialloc+0x679> 92499: 44 8b 05 00 00 00 00 mov 0x0(%rip),%r8d # 924a0 <xfs_dir_ialloc+0x660> 924a0: 45 85 c0 test %r8d,%r8d 924a3: 74 14 je 924b9 <xfs_dir_ialloc+0x679> 924a5: 83 c9 40 or $0x40,%ecx 924a8: 66 41 89 8d 16 01 00 mov %cx,0x116(%r13) 924af: 00 924b0: 41 0f b7 84 24 16 01 movzwl 0x116(%r12),%eax 924b7: 00 00 924b9: a8 80 test $0x80,%al Roughly, the main difference here IMHO, is the fact the current code uses xor to zero out the registers prior test/copying the flags into it, while using the patch applied, this is replaced by movz instructions since it copies the value's flag directly from the xfs_inode struct. So, IMHO I don't really see enough difference to justify dropping this patch. Anyway, as I mentioned, my ASM is a bit rusty, so take it with a pinch of salt :), but from my side, you can add: Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com> Cheers.
On Tue, Jun 01, 2021 at 09:33:15AM +1000, Dave Chinner wrote: > On Mon, May 31, 2021 at 03:40:38PM -0700, Darrick J. Wong wrote: > > From: Darrick J. Wong <djwong@kernel.org> > > > > Remove the unnecessary convenience variable. > > > > Signed-off-by: Darrick J. Wong <djwong@kernel.org> > > --- > > fs/xfs/xfs_inode.c | 25 +++++++++++-------------- > > 1 file changed, 11 insertions(+), 14 deletions(-) > > > > > > diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c > > index e4c2da4566f1..1e28997c6f78 100644 > > --- a/fs/xfs/xfs_inode.c > > +++ b/fs/xfs/xfs_inode.c > > @@ -689,47 +689,44 @@ xfs_inode_inherit_flags( > > struct xfs_inode *ip, > > const struct xfs_inode *pip) > > { > > - unsigned int di_flags = 0; > > xfs_failaddr_t failaddr; > > umode_t mode = VFS_I(ip)->i_mode; > > > > if (S_ISDIR(mode)) { > > if (pip->i_diflags & XFS_DIFLAG_RTINHERIT) > > - di_flags |= XFS_DIFLAG_RTINHERIT; > > + ip->i_diflags |= XFS_DIFLAG_RTINHERIT; > > if (pip->i_diflags & XFS_DIFLAG_EXTSZINHERIT) { > > - di_flags |= XFS_DIFLAG_EXTSZINHERIT; > > + ip->i_diflags |= XFS_DIFLAG_EXTSZINHERIT; > > ip->i_extsize = pip->i_extsize; > > } > > Hmmmm. > > IIRC, these functions were originally written this way because the > compiler generated much better code using a local variable than when > writing directly to the ip->i_d.di_flags. Is this still true now? > I think it's worth checking, because we have changed the structure > of the xfs_inode (removed the i_d structure) so maybe this isn't a > concern anymore? Before the patch, the extszinherit code emitted on my system (gcc 10.2) looked like this (0x15c is the offset of i_extsize and 0x166 is the offset of i_diflags): 699 if (pip->i_diflags & XFS_DIFLAG_EXTSZINHERIT) { 0xffffffffa0375715 <+1909>: test $0x10,%ah 0xffffffffa0375718 <+1912>: jne 0xffffffffa0375759 <xfs_dir_ialloc+1977> 0xffffffffa037571a <+1914>: mov 0x15c(%r13),%esi 700 di_flags |= XFS_DIFLAG_EXTSZINHERIT; 0xffffffffa0375759 <+1977>: mov 0x15c(%r12),%esi 0xffffffffa0375761 <+1985>: or $0x10,%ch 701 ip->i_extsize = pip->i_extsize; 0xffffffffa0375764 <+1988>: mov %esi,0x15c(%r13) 0xffffffffa037576b <+1995>: movzwl 0x166(%r12),%eax 0xffffffffa0375774 <+2004>: jmp 0xffffffffa0375721 <xfs_dir_ialloc+1921> 702 } 703 if (pip->i_diflags & XFS_DIFLAG_PROJINHERIT) 0xffffffffa0375721 <+1921>: mov %ecx,%r8d 0xffffffffa0375724 <+1924>: or $0x200,%r8d 0xffffffffa037572b <+1931>: test $0x2,%ah 0xffffffffa037572e <+1934>: cmovne %r8d,%ecx 0xffffffffa0375732 <+1938>: jmpq 0xffffffffa03755e7 <xfs_dir_ialloc+1607> 704 di_flags |= XFS_DIFLAG_PROJINHERIT; 705 } else if (S_ISREG(mode)) { With a snippet at the bottom to copy %cx back to the inode: 730 di_flags |= XFS_DIFLAG_FILESTREAM; 731 732 ip->i_diflags |= di_flags; 0xffffffffa0375680 <+1760>: or 0x166(%r13),%cx 0xffffffffa0375688 <+1768>: mov %cx,0x166(%r13) With the patch applied, that code becomes: 698 if (pip->i_diflags & XFS_DIFLAG_EXTSZINHERIT) { 0xffffffffa0375751 <+1969>: test $0x10,%ah 0xffffffffa0375754 <+1972>: jne 0xffffffffa03757d0 <xfs_dir_ialloc+2096> 0xffffffffa0375756 <+1974>: mov 0x15c(%r13),%esi 699 ip->i_diflags |= XFS_DIFLAG_EXTSZINHERIT; 0xffffffffa03757d0 <+2096>: or $0x10,%ch 0xffffffffa03757d3 <+2099>: mov %cx,0x166(%r13) 700 ip->i_extsize = pip->i_extsize; 0xffffffffa03757db <+2107>: mov 0x15c(%r12),%esi 0xffffffffa03757e3 <+2115>: mov %esi,0x15c(%r13) 0xffffffffa03757ea <+2122>: movzwl 0x166(%r12),%eax 0xffffffffa03757f3 <+2131>: jmpq 0xffffffffa037575d <xfs_dir_ialloc+1981> 0xffffffffa03757f8 <+2136>: callq 0xffffffff81713cb0 <__stack_chk_fail> 0xffffffffa03757fd: nopl (%rax) 701 } 702 if (pip->i_diflags & XFS_DIFLAG_PROJINHERIT) 0xffffffffa037575d <+1981>: test $0x2,%ah 0xffffffffa0375760 <+1984>: je 0xffffffffa03755f2 <xfs_dir_ialloc+1618> 703 ip->i_diflags |= XFS_DIFLAG_PROJINHERIT; 0xffffffffa0375766 <+1990>: or $0x2,%ch 0xffffffffa0375769 <+1993>: mov %cx,0x166(%r13) 0xffffffffa0375771 <+2001>: movzwl 0x166(%r12),%eax 0xffffffffa037577a <+2010>: jmpq 0xffffffffa03755f2 <xfs_dir_ialloc+1618> 704 } else if (S_ISREG(mode)) { AFAICT the main difference between the two versions now is that the new version will copy %cx back to ip->i_diflags after every set operation, and the old version would sometimes use a conditional move to update %cx instead of a conditional branch. I suspect the old version /is/ more efficient on x86, but I didn't see any measurable difference between the two versions. Hm. The old code was 197 bytes vs. 243 for the new one, so fmeh, I'll drop this because I'd rather move on to the iwalk pre-cleanup cleanup series. --D > > Cheers, > > Dave. > -- > Dave Chinner > david@fromorbit.com
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c index e4c2da4566f1..1e28997c6f78 100644 --- a/fs/xfs/xfs_inode.c +++ b/fs/xfs/xfs_inode.c @@ -689,47 +689,44 @@ xfs_inode_inherit_flags( struct xfs_inode *ip, const struct xfs_inode *pip) { - unsigned int di_flags = 0; xfs_failaddr_t failaddr; umode_t mode = VFS_I(ip)->i_mode; if (S_ISDIR(mode)) { if (pip->i_diflags & XFS_DIFLAG_RTINHERIT) - di_flags |= XFS_DIFLAG_RTINHERIT; + ip->i_diflags |= XFS_DIFLAG_RTINHERIT; if (pip->i_diflags & XFS_DIFLAG_EXTSZINHERIT) { - di_flags |= XFS_DIFLAG_EXTSZINHERIT; + ip->i_diflags |= XFS_DIFLAG_EXTSZINHERIT; ip->i_extsize = pip->i_extsize; } if (pip->i_diflags & XFS_DIFLAG_PROJINHERIT) - di_flags |= XFS_DIFLAG_PROJINHERIT; + ip->i_diflags |= XFS_DIFLAG_PROJINHERIT; } else if (S_ISREG(mode)) { if ((pip->i_diflags & XFS_DIFLAG_RTINHERIT) && xfs_sb_version_hasrealtime(&ip->i_mount->m_sb)) - di_flags |= XFS_DIFLAG_REALTIME; + ip->i_diflags |= XFS_DIFLAG_REALTIME; if (pip->i_diflags & XFS_DIFLAG_EXTSZINHERIT) { - di_flags |= XFS_DIFLAG_EXTSIZE; + ip->i_diflags |= XFS_DIFLAG_EXTSIZE; ip->i_extsize = pip->i_extsize; } } if ((pip->i_diflags & XFS_DIFLAG_NOATIME) && xfs_inherit_noatime) - di_flags |= XFS_DIFLAG_NOATIME; + ip->i_diflags |= XFS_DIFLAG_NOATIME; if ((pip->i_diflags & XFS_DIFLAG_NODUMP) && xfs_inherit_nodump) - di_flags |= XFS_DIFLAG_NODUMP; + ip->i_diflags |= XFS_DIFLAG_NODUMP; if ((pip->i_diflags & XFS_DIFLAG_SYNC) && xfs_inherit_sync) - di_flags |= XFS_DIFLAG_SYNC; + ip->i_diflags |= XFS_DIFLAG_SYNC; if ((pip->i_diflags & XFS_DIFLAG_NOSYMLINKS) && xfs_inherit_nosymlinks) - di_flags |= XFS_DIFLAG_NOSYMLINKS; + ip->i_diflags |= XFS_DIFLAG_NOSYMLINKS; if ((pip->i_diflags & XFS_DIFLAG_NODEFRAG) && xfs_inherit_nodefrag) - di_flags |= XFS_DIFLAG_NODEFRAG; + ip->i_diflags |= XFS_DIFLAG_NODEFRAG; if (pip->i_diflags & XFS_DIFLAG_FILESTREAM) - di_flags |= XFS_DIFLAG_FILESTREAM; - - ip->i_diflags |= di_flags; + ip->i_diflags |= XFS_DIFLAG_FILESTREAM; /* * Inode verifiers on older kernels only check that the extent size