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From ac5c35e60743b4260df777cc4ac1e877c2999b1d Mon Sep 17 00:00:00 2001
From: Kyle Huey <me@kylehuey.com>
Date: Tue, 14 Feb 2017 00:11:02 -0800
Subject: [PATCH 35/93] x86/process: Optimize TIF checks in __switch_to_xtra()
commit af8b3cd3934ec60f4c2a420d19a9d416554f140b upstream
Help the compiler to avoid reevaluating the thread flags for each checked
bit by reordering the bit checks and providing an explicit xor for
evaluation.
With default defconfigs for each arch,
x86_64: arch/x86/kernel/process.o
text data bss dec hex
3056 8577 16 11649 2d81 Before
3024 8577 16 11617 2d61 After
i386: arch/x86/kernel/process.o
text data bss dec hex
2957 8673 8 11638 2d76 Before
2925 8673 8 11606 2d56 After
Originally-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Kyle Huey <khuey@kylehuey.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Link: http://lkml.kernel.org/r/20170214081104.9244-2-khuey@kylehuey.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[dwmw2: backported to make TIF_RDS handling simpler.
No deferred TR reload.]
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kernel/process.c | 54 +++++++++++++++++++++++++++--------------------
1 file changed, 31 insertions(+), 23 deletions(-)
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index a55b320..0e1999e 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -192,48 +192,56 @@ int set_tsc_mode(unsigned int val)
return 0;
}
+static inline void switch_to_bitmap(struct tss_struct *tss,
+ struct thread_struct *prev,
+ struct thread_struct *next,
+ unsigned long tifp, unsigned long tifn)
+{
+ if (tifn & _TIF_IO_BITMAP) {
+ /*
+ * Copy the relevant range of the IO bitmap.
+ * Normally this is 128 bytes or less:
+ */
+ memcpy(tss->io_bitmap, next->io_bitmap_ptr,
+ max(prev->io_bitmap_max, next->io_bitmap_max));
+ } else if (tifp & _TIF_IO_BITMAP) {
+ /*
+ * Clear any possible leftover bits:
+ */
+ memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
+ }
+}
+
void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p,
struct tss_struct *tss)
{
struct thread_struct *prev, *next;
+ unsigned long tifp, tifn;
prev = &prev_p->thread;
next = &next_p->thread;
- if (test_tsk_thread_flag(prev_p, TIF_BLOCKSTEP) ^
- test_tsk_thread_flag(next_p, TIF_BLOCKSTEP)) {
+ tifn = READ_ONCE(task_thread_info(next_p)->flags);
+ tifp = READ_ONCE(task_thread_info(prev_p)->flags);
+ switch_to_bitmap(tss, prev, next, tifp, tifn);
+
+ propagate_user_return_notify(prev_p, next_p);
+
+ if ((tifp ^ tifn) & _TIF_BLOCKSTEP) {
unsigned long debugctl = get_debugctlmsr();
debugctl &= ~DEBUGCTLMSR_BTF;
- if (test_tsk_thread_flag(next_p, TIF_BLOCKSTEP))
+ if (tifn & _TIF_BLOCKSTEP)
debugctl |= DEBUGCTLMSR_BTF;
-
update_debugctlmsr(debugctl);
}
- if (test_tsk_thread_flag(prev_p, TIF_NOTSC) ^
- test_tsk_thread_flag(next_p, TIF_NOTSC)) {
- /* prev and next are different */
- if (test_tsk_thread_flag(next_p, TIF_NOTSC))
+ if ((tifp ^ tifn) & _TIF_NOTSC) {
+ if (tifn & _TIF_NOTSC)
hard_disable_TSC();
else
hard_enable_TSC();
}
-
- if (test_tsk_thread_flag(next_p, TIF_IO_BITMAP)) {
- /*
- * Copy the relevant range of the IO bitmap.
- * Normally this is 128 bytes or less:
- */
- memcpy(tss->io_bitmap, next->io_bitmap_ptr,
- max(prev->io_bitmap_max, next->io_bitmap_max));
- } else if (test_tsk_thread_flag(prev_p, TIF_IO_BITMAP)) {
- /*
- * Clear any possible leftover bits:
- */
- memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
- }
- propagate_user_return_notify(prev_p, next_p);
}
/*
--
2.7.4
|
