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  1. 10 Oct, 2023 1 commit
  3. 09 Oct, 2023 4 commits
    • Uros Bizjak's avatar
      locking/atomic, xen: Use sync_try_cmpxchg() instead of sync_cmpxchg() · ad0a2e4c
      Uros Bizjak authored 
      Use sync_try_cmpxchg() instead of sync_cmpxchg(*ptr, old, new) == old
in clear_masked_cond(), clear_linked() and
gnttab_end_foreign_access_ref_v1(). x86 CMPXCHG instruction returns
success in ZF flag, so this change saves a compare after cmpxchg
(and related move instruction in front of cmpxchg), improving the
cmpxchg loop in gnttab_end_foreign_access_ref_v1() from:

     174:	eb 0e                	jmp    184 <...>
     176:	89 d0                	mov    %edx,%eax
     178:	f0 66 0f b1 31       	lock cmpxchg %si,(%rcx)
     17d:	66 39 c2             	cmp    %ax,%dx
     180:	74 11                	je     193 <...>
     182:	89 c2                	mov    %eax,%edx
     184:	89 d6                	mov    %edx,%esi
     186:	66 83 e6 18          	and    $0x18,%si
     18a:	74 ea                	je     176 <...>

to:

     614:	89 c1                	mov    %eax,%ecx
     616:	66 83 e1 18          	and    $0x18,%cx
     61a:	75 11                	jne    62d <...>
     61c:	f0 66 0f b1 0a       	lock cmpxchg %cx,(%rdx)
     621:	75 f1                	jne    614 <...>

No functional change intended.
Signed-off-by: default avatarUros Bizjak <ubizjak@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Acked-by: default avatarJuergen Gross <jgross@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org
      ad0a2e4c
    • Uros Bizjak's avatar
      locking/atomic/x86: Introduce arch_sync_try_cmpxchg() · 636d6a8b
      Uros Bizjak authored 
      Introduce the arch_sync_try_cmpxchg() macro to improve code using
sync_try_cmpxchg() locking primitive. The new definitions use existing
__raw_try_cmpxchg() macros, but use its own "lock; " prefix.

The new macros improve assembly of the cmpxchg loop in
evtchn_fifo_unmask() from drivers/xen/events/events_fifo.c from:

 57a:	85 c0                	test   %eax,%eax
 57c:	78 52                	js     5d0 <...>
 57e:	89 c1                	mov    %eax,%ecx
 580:	25 ff ff ff af       	and    $0xafffffff,%eax
 585:	c7 04 24 00 00 00 00 	movl   $0x0,(%rsp)
 58c:	81 e1 ff ff ff ef    	and    $0xefffffff,%ecx
 592:	89 4c 24 04          	mov    %ecx,0x4(%rsp)
 596:	89 44 24 08          	mov    %eax,0x8(%rsp)
 59a:	8b 74 24 08          	mov    0x8(%rsp),%esi
 59e:	8b 44 24 04          	mov    0x4(%rsp),%eax
 5a2:	f0 0f b1 32          	lock cmpxchg %esi,(%rdx)
 5a6:	89 04 24             	mov    %eax,(%rsp)
 5a9:	8b 04 24             	mov    (%rsp),%eax
 5ac:	39 c1                	cmp    %eax,%ecx
 5ae:	74 07                	je     5b7 <...>
 5b0:	a9 00 00 00 40       	test   $0x40000000,%eax
 5b5:	75 c3                	jne    57a <...>
 <...>

to:

 578:	a9 00 00 00 40       	test   $0x40000000,%eax
 57d:	74 2b                	je     5aa <...>
 57f:	85 c0                	test   %eax,%eax
 581:	78 40                	js     5c3 <...>
 583:	89 c1                	mov    %eax,%ecx
 585:	25 ff ff ff af       	and    $0xafffffff,%eax
 58a:	81 e1 ff ff ff ef    	and    $0xefffffff,%ecx
 590:	89 4c 24 04          	mov    %ecx,0x4(%rsp)
 594:	89 44 24 08          	mov    %eax,0x8(%rsp)
 598:	8b 4c 24 08          	mov    0x8(%rsp),%ecx
 59c:	8b 44 24 04          	mov    0x4(%rsp),%eax
 5a0:	f0 0f b1 0a          	lock cmpxchg %ecx,(%rdx)
 5a4:	89 44 24 04          	mov    %eax,0x4(%rsp)
 5a8:	75 30                	jne    5da <...>
 <...>
 5da:	8b 44 24 04          	mov    0x4(%rsp),%eax
 5de:	eb 98                	jmp    578 <...>

The new code removes move instructions from 585: 5a6: and 5a9:
and the compare from 5ac:. Additionally, the compiler assumes that
cmpxchg success is more probable and optimizes code flow accordingly.
Signed-off-by: default avatarUros Bizjak <ubizjak@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org
      636d6a8b
    • Uros Bizjak's avatar
      locking/atomic: Add generic support for sync_try_cmpxchg() and its fallback · e01cc1e8
      Uros Bizjak authored 
      Provide the generic sync_try_cmpxchg() function from the
raw_ prefixed version, also adding explicit instrumentation.

The patch amends existing scripts to generate sync_try_cmpxchg()
locking primitive and its raw_sync_try_cmpxchg() fallback, while
leaving existing macros from the try_cmpxchg() family unchanged.

The target can define its own arch_sync_try_cmpxchg() to override the
generic version of raw_sync_try_cmpxchg(). This allows the target
to generate more optimal assembly than the generic version.

Additionally, the patch renames two scripts to better reflect
whet they really do.
Signed-off-by: default avatarUros Bizjak <ubizjak@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org
      e01cc1e8
    • Ingo Molnar's avatar
      Merge tag 'v6.6-rc5' into locking/core, to pick up fixes · fdb8b7a1
      Ingo Molnar authored 
      Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
      fdb8b7a1
  5. 08 Oct, 2023 4 commits
  7. 07 Oct, 2023 10 commits
  9. 06 Oct, 2023 21 commits
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