diff options
| author | Uros Bizjak <ubizjak@gmail.com> | 2023-07-10 22:01:27 +0300 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2023-10-09 19:14:34 +0300 |
| commit | ad0a2e4c2f20510d7e3f2bc110cf74f8578547f0 (patch) | |
| tree | 0f5fe98b87c809da5a0fcf44691ece720caf5ab1 /drivers/xen/grant-table.c | |
| parent | 636d6a8b850a2bb8462b5f743c9db9aa4d735cda (diff) | |
| download | linux-ad0a2e4c2f20510d7e3f2bc110cf74f8578547f0.tar.xz | |
locking/atomic, xen: Use sync_try_cmpxchg() instead of sync_cmpxchg()
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: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Juergen 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
Diffstat (limited to 'drivers/xen/grant-table.c')
| -rw-r--r-- | drivers/xen/grant-table.c | 10 |
1 files changed, 4 insertions, 6 deletions
diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c index 35659bf70746..04a6b470b15d 100644 --- a/drivers/xen/grant-table.c +++ b/drivers/xen/grant-table.c @@ -427,16 +427,14 @@ EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access); static int gnttab_end_foreign_access_ref_v1(grant_ref_t ref) { - u16 flags, nflags; - u16 *pflags; + u16 *pflags = &gnttab_shared.v1[ref].flags; + u16 flags; - pflags = &gnttab_shared.v1[ref].flags; - nflags = *pflags; + flags = *pflags; do { - flags = nflags; if (flags & (GTF_reading|GTF_writing)) return 0; - } while ((nflags = sync_cmpxchg(pflags, flags, 0)) != flags); + } while (!sync_try_cmpxchg(pflags, &flags, 0)); return 1; } |