diff mbox series

[V2,09/17] x86/entry: Remove _TIF_NOHZ from _TIF_WORK_SYSCALL_ENTRY

Message ID 20191023123118.491328859@linutronix.de (mailing list archive)
State New, archived
Headers show
Series entry: Provide generic implementation for host and guest entry/exit work | expand

Commit Message

Thomas Gleixner Oct. 23, 2019, 12:27 p.m. UTC 
From: Thomas Gleixner <tglx@linutronix.de>

Evaluating _TIF_NOHZ to decide whether to use the slow syscall entry path
is not only pointless, it's actually counterproductive:

 1) Context tracking code is invoked unconditionally before that flag is
    evaluated.

 2) If the flag is set the slow path is invoked for nothing due to #1

Remove it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/include/asm/thread_info.h |    8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

Comments

Frederic Weisbecker Jan. 6, 2020, 4:11 a.m. UTC | #1 
On Wed, Oct 23, 2019 at 02:27:14PM +0200, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
> 
> Evaluating _TIF_NOHZ to decide whether to use the slow syscall entry path
> is not only pointless, it's actually counterproductive:
> 
>  1) Context tracking code is invoked unconditionally before that flag is
>     evaluated.
> 
>  2) If the flag is set the slow path is invoked for nothing due to #1
> 
> Remove it.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

I'm borrowing this patch for a series of mine. But if you apply
it in the meantime, that would be even better :-)

Thanks!
diff mbox series

Patch

--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -133,14 +133,10 @@  struct thread_info {
 #define _TIF_X32		(1 << TIF_X32)
 #define _TIF_FSCHECK		(1 << TIF_FSCHECK)
 
-/*
- * work to do in syscall_trace_enter().  Also includes TIF_NOHZ for
- * enter_from_user_mode()
- */
+/* Work to do before invoking the actual syscall. */
 #define _TIF_WORK_SYSCALL_ENTRY	\
 	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_EMU | _TIF_SYSCALL_AUDIT |	\
-	 _TIF_SECCOMP | _TIF_SYSCALL_TRACEPOINT |	\
-	 _TIF_NOHZ)
+	 _TIF_SECCOMP | _TIF_SYSCALL_TRACEPOINT)
 
 /* flags to check in __switch_to() */
 #define _TIF_WORK_CTXSW_BASE						\