[RFC PATCH REBASED 0/3] Move ARCH specific fpu_counter out of task_struct

[RFC PATCH REBASED 0/3] Move ARCH specific fpu_counter out of task_struct

[Vineet Gupta]

Hi,

This is a resend of the patches I sent last week which failed to draw any
attention.

This basically came up when ARC SMP 3.11 failed to build due to a ST insn
dealing with task_struct.thread going out of range.

When staring at code I spotted @fpu_counter in task_struct which only SH/x86
happen to use, and can be easily moved out into corresponding ARCH specific
thread_struct. This saves 4 bytes per task_struct instantiated, for all the
other 18 arches.

One of the resistance to the patch(es) could be that task_struct fields were at
some point arranged to reduce the number of line misses. However there is lot
of variance there due to so many #ifdefs, variable size of cpumask (>32 cores..)
etc, so that argument alone might not be sufficient vs. saving 4 bytes per
instance.

Comments please !

Thx,
-Vineet

Vineet Gupta (3):
  sh: Move fpu_counter into ARCH specific thread_struct
  x86: Move fpu_counter into ARCH specific thread_struct
  sched: Remove ARCH specific fpu_counter from task_struct

 arch/sh/include/asm/fpu.h           |  2 +-
 arch/sh/include/asm/processor_32.h  | 10 ++++++++++
 arch/sh/include/asm/processor_64.h  | 10 ++++++++++
 arch/sh/kernel/cpu/fpu.c            |  2 +-
 arch/sh/kernel/process_32.c         |  6 +++---
 arch/x86/include/asm/fpu-internal.h | 10 +++++-----
 arch/x86/include/asm/processor.h    |  9 +++++++++
 arch/x86/kernel/i387.c              |  2 +-
 arch/x86/kernel/process_32.c        |  4 ++--
 arch/x86/kernel/process_64.c        |  2 +-
 arch/x86/kernel/traps.c             |  2 +-
 include/linux/sched.h               |  9 ---------
 12 files changed, 44 insertions(+), 24 deletions(-)

-- 
1.8.1.2

[RFC PATCH REBASED 1/3] sh: Move fpu_counter into ARCH specific thread_struct

[Vineet Gupta]

Only a couple of arches (sh/x86) use fpu_counter in task_struct so it
can be moved out into ARCH specific thread_struct, reducing the size of
task_struct for other arches.

Compile tested sh defconfig + sh4-linux-gcc (4.6.3)

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jesper Nilsson <jesper.nilsson@axis.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: linux-kernel@vger.kernel.org
Cc: linux-arch@vger.kernel.org
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-sh@vger.kernel.org
---
 arch/sh/include/asm/fpu.h          |  2 +-
 arch/sh/include/asm/processor_32.h | 10 ++++++++++
 arch/sh/include/asm/processor_64.h | 10 ++++++++++
 arch/sh/kernel/cpu/fpu.c           |  2 +-
 arch/sh/kernel/process_32.c        |  6 +++---
 5 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/arch/sh/include/asm/fpu.h b/arch/sh/include/asm/fpu.h
index 06c4281..09fc2bc 100644
--- a/arch/sh/include/asm/fpu.h
+++ b/arch/sh/include/asm/fpu.h
@@ -46,7 +46,7 @@ static inline void __unlazy_fpu(struct task_struct *tsk, struct pt_regs *regs)
 		save_fpu(tsk);
 		release_fpu(regs);
 	} else
-		tsk->fpu_counter = 0;
+		tsk->thread.fpu_counter = 0;
 }
 
 static inline void unlazy_fpu(struct task_struct *tsk, struct pt_regs *regs)
diff --git a/arch/sh/include/asm/processor_32.h b/arch/sh/include/asm/processor_32.h
index e699a12..18e0377 100644
--- a/arch/sh/include/asm/processor_32.h
+++ b/arch/sh/include/asm/processor_32.h
@@ -111,6 +111,16 @@ struct thread_struct {
 
 	/* Extended processor state */
 	union thread_xstate *xstate;
+
+	/*
+	 * fpu_counter contains the number of consecutive context switches
+	 * that the FPU is used. If this is over a threshold, the lazy fpu
+	 * saving becomes unlazy to save the trap. This is an unsigned char
+	 * so that after 256 times the counter wraps and the behavior turns
+	 * lazy again; this to deal with bursty apps that only use FPU for
+	 * a short time
+	 */
+	unsigned char fpu_counter;
 };
 
 #define INIT_THREAD  {						\
diff --git a/arch/sh/include/asm/processor_64.h b/arch/sh/include/asm/processor_64.h
index 1cc7d31..eedd4f6 100644
--- a/arch/sh/include/asm/processor_64.h
+++ b/arch/sh/include/asm/processor_64.h
@@ -126,6 +126,16 @@ struct thread_struct {
 
 	/* floating point info */
 	union thread_xstate *xstate;
+
+	/*
+	 * fpu_counter contains the number of consecutive context switches
+	 * that the FPU is used. If this is over a threshold, the lazy fpu
+	 * saving becomes unlazy to save the trap. This is an unsigned char
+	 * so that after 256 times the counter wraps and the behavior turns
+	 * lazy again; this to deal with bursty apps that only use FPU for
+	 * a short time
+	 */
+	unsigned char fpu_counter;
 };
 
 #define INIT_MMAP \
diff --git a/arch/sh/kernel/cpu/fpu.c b/arch/sh/kernel/cpu/fpu.c
index f8f7af5..4e33224 100644
--- a/arch/sh/kernel/cpu/fpu.c
+++ b/arch/sh/kernel/cpu/fpu.c
@@ -44,7 +44,7 @@ void __fpu_state_restore(void)
 	restore_fpu(tsk);
 
 	task_thread_info(tsk)->status |= TS_USEDFPU;
-	tsk->fpu_counter++;
+	tsk->thread.fpu_counter++;
 }
 
 void fpu_state_restore(struct pt_regs *regs)
diff --git a/arch/sh/kernel/process_32.c b/arch/sh/kernel/process_32.c
index ebd3933..2885fc9 100644
--- a/arch/sh/kernel/process_32.c
+++ b/arch/sh/kernel/process_32.c
@@ -156,7 +156,7 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
 #endif
 		ti->addr_limit = KERNEL_DS;
 		ti->status &= ~TS_USEDFPU;
-		p->fpu_counter = 0;
+		p->thread.fpu_counter = 0;
 		return 0;
 	}
 	*childregs = *current_pt_regs();
@@ -189,7 +189,7 @@ __switch_to(struct task_struct *prev, struct task_struct *next)
 	unlazy_fpu(prev, task_pt_regs(prev));
 
 	/* we're going to use this soon, after a few expensive things */
-	if (next->fpu_counter > 5)
+	if (next->thread.fpu_counter > 5)
 		prefetch(next_t->xstate);
 
 #ifdef CONFIG_MMU
@@ -207,7 +207,7 @@ __switch_to(struct task_struct *prev, struct task_struct *next)
 	 * restore of the math state immediately to avoid the trap; the
 	 * chances of needing FPU soon are obviously high now
 	 */
-	if (next->fpu_counter > 5)
+	if (next->thread.fpu_counter > 5)
 		__fpu_state_restore();
 
 	return prev;
-- 
1.8.1.2

[RFC PATCH REBASED 2/3] x86: Move fpu_counter into ARCH specific thread_struct

[Vineet Gupta]

Only a couple of arches (sh/x86) use fpu_counter in task_struct so it
can be moved out into ARCH specific thread_struct, reducing the size of
task_struct for other arches.

Compile tested i386_defconfig + gcc 4.7.3

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Vincent Palatin <vpalatin@chromium.org>
Cc: Len Brown <len.brown@intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Pekka Riikonen <priikone@iki.fi>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Jones <davej@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org
---
 arch/x86/include/asm/fpu-internal.h | 10 +++++-----
 arch/x86/include/asm/processor.h    |  9 +++++++++
 arch/x86/kernel/i387.c              |  2 +-
 arch/x86/kernel/process_32.c        |  4 ++--
 arch/x86/kernel/process_64.c        |  2 +-
 arch/x86/kernel/traps.c             |  2 +-
 6 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h
index 4d0bda7..c49a613 100644
--- a/arch/x86/include/asm/fpu-internal.h
+++ b/arch/x86/include/asm/fpu-internal.h
@@ -365,7 +365,7 @@ static inline void drop_fpu(struct task_struct *tsk)
 	 * Forget coprocessor state..
 	 */
 	preempt_disable();
-	tsk->fpu_counter = 0;
+	tsk->thread.fpu_counter = 0;
 	__drop_fpu(tsk);
 	clear_used_math();
 	preempt_enable();
@@ -424,7 +424,7 @@ static inline fpu_switch_t switch_fpu_prepare(struct task_struct *old, struct ta
 	 * or if the past 5 consecutive context-switches used math.
 	 */
 	fpu.preload = tsk_used_math(new) && (use_eager_fpu() ||
-					     new->fpu_counter > 5);
+					     new->thread.fpu_counter > 5);
 	if (__thread_has_fpu(old)) {
 		if (!__save_init_fpu(old))
 			cpu = ~0;
@@ -433,16 +433,16 @@ static inline fpu_switch_t switch_fpu_prepare(struct task_struct *old, struct ta
 
 		/* Don't change CR0.TS if we just switch! */
 		if (fpu.preload) {
-			new->fpu_counter++;
+			new->thread.fpu_counter++;
 			__thread_set_has_fpu(new);
 			prefetch(new->thread.fpu.state);
 		} else if (!use_eager_fpu())
 			stts();
 	} else {
-		old->fpu_counter = 0;
+		old->thread.fpu_counter = 0;
 		old->thread.fpu.last_cpu = ~0;
 		if (fpu.preload) {
-			new->fpu_counter++;
+			new->thread.fpu_counter++;
 			if (!use_eager_fpu() && fpu_lazy_restore(new, cpu))
 				fpu.preload = 0;
 			else
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 987c75e..7b034a4 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -488,6 +488,15 @@ struct thread_struct {
 	unsigned long		iopl;
 	/* Max allowed port in the bitmap, in bytes: */
 	unsigned		io_bitmap_max;
+	/*
+	 * fpu_counter contains the number of consecutive context switches
+	 * that the FPU is used. If this is over a threshold, the lazy fpu
+	 * saving becomes unlazy to save the trap. This is an unsigned char
+	 * so that after 256 times the counter wraps and the behavior turns
+	 * lazy again; this to deal with bursty apps that only use FPU for
+	 * a short time
+	 */
+	unsigned char fpu_counter;
 };
 
 /*
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index 5d576ab..e8368c6 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -100,7 +100,7 @@ void unlazy_fpu(struct task_struct *tsk)
 		__save_init_fpu(tsk);
 		__thread_fpu_end(tsk);
 	} else
-		tsk->fpu_counter = 0;
+		tsk->thread.fpu_counter = 0;
 	preempt_enable();
 }
 EXPORT_SYMBOL(unlazy_fpu);
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 884f98f..6af43b0 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -153,7 +153,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
 		childregs->orig_ax = -1;
 		childregs->cs = __KERNEL_CS | get_kernel_rpl();
 		childregs->flags = X86_EFLAGS_IF | X86_EFLAGS_FIXED;
-		p->fpu_counter = 0;
+		p->thread.fpu_counter = 0;
 		p->thread.io_bitmap_ptr = NULL;
 		memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));
 		return 0;
@@ -166,7 +166,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
 	p->thread.ip = (unsigned long) ret_from_fork;
 	task_user_gs(p) = get_user_gs(current_pt_regs());
 
-	p->fpu_counter = 0;
+	p->thread.fpu_counter = 0;
 	p->thread.io_bitmap_ptr = NULL;
 	tsk = current;
 	err = -ENOMEM;
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index bb1dc51..bbab295 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -163,7 +163,7 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
 	p->thread.sp = (unsigned long) childregs;
 	p->thread.usersp = me->thread.usersp;
 	set_tsk_thread_flag(p, TIF_FORK);
-	p->fpu_counter = 0;
+	p->thread.fpu_counter = 0;
 	p->thread.io_bitmap_ptr = NULL;
 
 	savesegment(gs, p->thread.gsindex);
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 8c8093b..64b980f 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -653,7 +653,7 @@ void math_state_restore(void)
 		return;
 	}
 
-	tsk->fpu_counter++;
+	tsk->thread.fpu_counter++;
 }
 EXPORT_SYMBOL_GPL(math_state_restore);
 
-- 
1.8.1.2

[RFC PATCH REBASED 3/3] sched: Remove ARCH specific fpu_counter from task_struct

[Vineet Gupta]

fpu_counter in task_struct was used only by sh/x86.
Both of these now carry it in ARCH specific thread_struct, hence this
can now be removed from generic task_struct, shrinking it slightly for
other arches.

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
 include/linux/sched.h | 9 ---------
 1 file changed, 9 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 6682da3..78386c1 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1046,15 +1046,6 @@ struct task_struct {
 	struct hlist_head preempt_notifiers;
 #endif
 
-	/*
-	 * fpu_counter contains the number of consecutive context switches
-	 * that the FPU is used. If this is over a threshold, the lazy fpu
-	 * saving becomes unlazy to save the trap. This is an unsigned char
-	 * so that after 256 times the counter wraps and the behavior turns
-	 * lazy again; this to deal with bursty apps that only use FPU for
-	 * a short time
-	 */
-	unsigned char fpu_counter;
 #ifdef CONFIG_BLK_DEV_IO_TRACE
 	unsigned int btrace_seq;
 #endif
-- 
1.8.1.2

Re: [RFC PATCH REBASED 1/3] sh: Move fpu_counter into ARCH specific thread_struct

[Vineet Gupta]

Hi Paul/SH folks.

Would appreciate your ACK/NAK on this.

Thx,
-Vineet

On 09/17/2013 11:47 AM, Vineet Gupta wrote:
> Only a couple of arches (sh/x86) use fpu_counter in task_struct so it
> can be moved out into ARCH specific thread_struct, reducing the size of
> task_struct for other arches.
> 
> Compile tested sh defconfig + sh4-linux-gcc (4.6.3)
> 
> Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
> Cc: Paul Mundt <lethal@linux-sh.org>
> Cc: Michel Lespinasse <walken@google.com>
> Cc: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Jesper Nilsson <jesper.nilsson@axis.com>
> Cc: Chris Metcalf <cmetcalf@tilera.com>
> Cc: "David S. Miller" <davem@davemloft.net>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-arch@vger.kernel.org
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: linux-sh@vger.kernel.org
> ---
>  arch/sh/include/asm/fpu.h          |  2 +-
>  arch/sh/include/asm/processor_32.h | 10 ++++++++++
>  arch/sh/include/asm/processor_64.h | 10 ++++++++++
>  arch/sh/kernel/cpu/fpu.c           |  2 +-
>  arch/sh/kernel/process_32.c        |  6 +++---
>  5 files changed, 25 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/sh/include/asm/fpu.h b/arch/sh/include/asm/fpu.h
> index 06c4281..09fc2bc 100644
> --- a/arch/sh/include/asm/fpu.h
> +++ b/arch/sh/include/asm/fpu.h
> @@ -46,7 +46,7 @@ static inline void __unlazy_fpu(struct task_struct *tsk, struct pt_regs *regs)
>  		save_fpu(tsk);
>  		release_fpu(regs);
>  	} else
> -		tsk->fpu_counter = 0;
> +		tsk->thread.fpu_counter = 0;
>  }
>  
>  static inline void unlazy_fpu(struct task_struct *tsk, struct pt_regs *regs)
> diff --git a/arch/sh/include/asm/processor_32.h b/arch/sh/include/asm/processor_32.h
> index e699a12..18e0377 100644
> --- a/arch/sh/include/asm/processor_32.h
> +++ b/arch/sh/include/asm/processor_32.h
> @@ -111,6 +111,16 @@ struct thread_struct {
>  
>  	/* Extended processor state */
>  	union thread_xstate *xstate;
> +
> +	/*
> +	 * fpu_counter contains the number of consecutive context switches
> +	 * that the FPU is used. If this is over a threshold, the lazy fpu
> +	 * saving becomes unlazy to save the trap. This is an unsigned char
> +	 * so that after 256 times the counter wraps and the behavior turns
> +	 * lazy again; this to deal with bursty apps that only use FPU for
> +	 * a short time
> +	 */
> +	unsigned char fpu_counter;
>  };
>  
>  #define INIT_THREAD  {						\
> diff --git a/arch/sh/include/asm/processor_64.h b/arch/sh/include/asm/processor_64.h
> index 1cc7d31..eedd4f6 100644
> --- a/arch/sh/include/asm/processor_64.h
> +++ b/arch/sh/include/asm/processor_64.h
> @@ -126,6 +126,16 @@ struct thread_struct {
>  
>  	/* floating point info */
>  	union thread_xstate *xstate;
> +
> +	/*
> +	 * fpu_counter contains the number of consecutive context switches
> +	 * that the FPU is used. If this is over a threshold, the lazy fpu
> +	 * saving becomes unlazy to save the trap. This is an unsigned char
> +	 * so that after 256 times the counter wraps and the behavior turns
> +	 * lazy again; this to deal with bursty apps that only use FPU for
> +	 * a short time
> +	 */
> +	unsigned char fpu_counter;
>  };
>  
>  #define INIT_MMAP \
> diff --git a/arch/sh/kernel/cpu/fpu.c b/arch/sh/kernel/cpu/fpu.c
> index f8f7af5..4e33224 100644
> --- a/arch/sh/kernel/cpu/fpu.c
> +++ b/arch/sh/kernel/cpu/fpu.c
> @@ -44,7 +44,7 @@ void __fpu_state_restore(void)
>  	restore_fpu(tsk);
>  
>  	task_thread_info(tsk)->status |= TS_USEDFPU;
> -	tsk->fpu_counter++;
> +	tsk->thread.fpu_counter++;
>  }
>  
>  void fpu_state_restore(struct pt_regs *regs)
> diff --git a/arch/sh/kernel/process_32.c b/arch/sh/kernel/process_32.c
> index ebd3933..2885fc9 100644
> --- a/arch/sh/kernel/process_32.c
> +++ b/arch/sh/kernel/process_32.c
> @@ -156,7 +156,7 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
>  #endif
>  		ti->addr_limit = KERNEL_DS;
>  		ti->status &= ~TS_USEDFPU;
> -		p->fpu_counter = 0;
> +		p->thread.fpu_counter = 0;
>  		return 0;
>  	}
>  	*childregs = *current_pt_regs();
> @@ -189,7 +189,7 @@ __switch_to(struct task_struct *prev, struct task_struct *next)
>  	unlazy_fpu(prev, task_pt_regs(prev));
>  
>  	/* we're going to use this soon, after a few expensive things */
> -	if (next->fpu_counter > 5)
> +	if (next->thread.fpu_counter > 5)
>  		prefetch(next_t->xstate);
>  
>  #ifdef CONFIG_MMU
> @@ -207,7 +207,7 @@ __switch_to(struct task_struct *prev, struct task_struct *next)
>  	 * restore of the math state immediately to avoid the trap; the
>  	 * chances of needing FPU soon are obviously high now
>  	 */
> -	if (next->fpu_counter > 5)
> +	if (next->thread.fpu_counter > 5)
>  		__fpu_state_restore();
>  
>  	return prev;
>