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

[Vineet Gupta <Vineet.Gupta1@synopsys.com>]

[+cc: x86 folks] as the mailer skipped the CC list.

On 09/17/2013 11:48 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 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);
>  
>