From: Michael Neuling <mikey@neuling•org>
To: Cyril Bur <cyrilbur@gmail•com>, linuxppc-dev@ozlabs•org
Subject: Re: [PATCH V2 6/8] powerpc: Add the ability to save FPU without giving it up
Date: Fri, 15 Jan 2016 17:08:55 +1100 [thread overview]
Message-ID: <1452838135.25634.39.camel@neuling.org> (raw)
In-Reply-To: <1452834254-22078-7-git-send-email-cyrilbur@gmail.com>
On Fri, 2016-01-15 at 16:04 +1100, Cyril Bur wrote:
> This patch adds the ability to be able to save the FPU registers to
> the
> thread struct without giving up (disabling the facility) next time
> the
> process returns to userspace.
>=20
> This patch optimises the thread copy path (as a result of a fork() or
> clone()) so that the parent thread can return to userspace with hot
> registers avoiding a possibly pointless reload of FPU register state.
This comment seems misleading. The patch seems to touch the VSX, VMX
and SPE state as well. =20
Mikey
>=20
> Signed-off-by: Cyril Bur <cyrilbur@gmail•com>
> ---
> arch/powerpc/include/asm/switch_to.h | 2 +-
> arch/powerpc/kernel/fpu.S | 21 ++++------------
> arch/powerpc/kernel/process.c | 46
> +++++++++++++++++++++++++++++++++++-
> 3 files changed, 50 insertions(+), 19 deletions(-)
>=20
> diff --git a/arch/powerpc/include/asm/switch_to.h
> b/arch/powerpc/include/asm/switch_to.h
> index 5b268b6..c4d50e9 100644
> --- a/arch/powerpc/include/asm/switch_to.h
> +++ b/arch/powerpc/include/asm/switch_to.h
> @@ -28,7 +28,7 @@ extern void giveup_all(struct task_struct *);
> extern void enable_kernel_fp(void);
> extern void flush_fp_to_thread(struct task_struct *);
> extern void giveup_fpu(struct task_struct *);
> -extern void __giveup_fpu(struct task_struct *);
> +extern void save_fpu(struct task_struct *);
> static inline void disable_kernel_fp(void)
> {
> msr_check_and_clear(MSR_FP);
> diff --git a/arch/powerpc/kernel/fpu.S b/arch/powerpc/kernel/fpu.S
> index b063524..15da2b5 100644
> --- a/arch/powerpc/kernel/fpu.S
> +++ b/arch/powerpc/kernel/fpu.S
> @@ -143,33 +143,20 @@ END_FTR_SECTION_IFSET(CPU_FTR_VSX)
> blr
> =20
> /*
> - * __giveup_fpu(tsk)
> - * Disable FP for the task given as the argument,
> - * and save the floating-point registers in its thread_struct.
> + * save_fpu(tsk)
> + * Save the floating-point registers in its thread_struct.
> * Enables the FPU for use in the kernel on return.
> */
> -_GLOBAL(__giveup_fpu)
> +_GLOBAL(save_fpu)
> addi r3,r3,THREAD /* want THREAD of
> task */
> PPC_LL r6,THREAD_FPSAVEAREA(r3)
> PPC_LL r5,PT_REGS(r3)
> PPC_LCMPI 0,r6,0
> bne 2f
> addi r6,r3,THREAD_FPSTATE
> -2: PPC_LCMPI 0,r5,0
> - SAVE_32FPVSRS(0, R4, R6)
> +2: SAVE_32FPVSRS(0, R4, R6)
> mffs fr0
> stfd fr0,FPSTATE_FPSCR(r6)
> - beq 1f
> - PPC_LL r4,_MSR-STACK_FRAME_OVERHEAD(r5)
> - li r3,MSR_FP|MSR_FE0|MSR_FE1
> -#ifdef CONFIG_VSX
> -BEGIN_FTR_SECTION
> - oris r3,r3,MSR_VSX@h
> -END_FTR_SECTION_IFSET(CPU_FTR_VSX)
> -#endif
> - andc r4,r4,r3 /* disable FP for
> previous task */
> - PPC_STL r4,_MSR-STACK_FRAME_OVERHEAD(r5)
> -1:
> blr
> =20
> /*
> diff --git a/arch/powerpc/kernel/process.c
> b/arch/powerpc/kernel/process.c
> index ec53468..8a96e4f 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -133,6 +133,16 @@ void __msr_check_and_clear(unsigned long bits)
> EXPORT_SYMBOL(__msr_check_and_clear);
> =20
> #ifdef CONFIG_PPC_FPU
> +void __giveup_fpu(struct task_struct *tsk)
> +{
> + save_fpu(tsk);
> + tsk->thread.regs->msr &=3D ~MSR_FP;
> +#ifdef CONFIG_VSX
> + if (cpu_has_feature(CPU_FTR_VSX))
> + tsk->thread.regs->msr &=3D ~MSR_VSX;
> +#endif
> +}
> +
> void giveup_fpu(struct task_struct *tsk)
> {
> check_if_tm_restore_required(tsk);
> @@ -421,12 +431,46 @@ void restore_math(struct pt_regs *regs)
> regs->msr =3D msr;
> }
> =20
> +void save_all(struct task_struct *tsk)
> +{
> + unsigned long usermsr;
> +
> + if (!tsk->thread.regs)
> + return;
> +
> + usermsr =3D tsk->thread.regs->msr;
> +
> + if ((usermsr & msr_all_available) =3D=3D 0)
> + return;
> +
> + msr_check_and_set(msr_all_available);
> +
> +#ifdef CONFIG_PPC_FPU
> + if (usermsr & MSR_FP)
> + save_fpu(tsk);
> +#endif
> +#ifdef CONFIG_ALTIVEC
> + if (usermsr & MSR_VEC)
> + __giveup_altivec(tsk);
> +#endif
> +#ifdef CONFIG_VSX
> + if (usermsr & MSR_VSX)
> + __giveup_vsx(tsk);
> +#endif
> +#ifdef CONFIG_SPE
> + if (usermsr & MSR_SPE)
> + __giveup_spe(tsk);
> +#endif
> +
> + msr_check_and_clear(msr_all_available);
> +}
> +
> void flush_all_to_thread(struct task_struct *tsk)
> {
> if (tsk->thread.regs) {
> preempt_disable();
> BUG_ON(tsk !=3D current);
> - giveup_all(tsk);
> + save_all(tsk);
> =20
> #ifdef CONFIG_SPE
> if (tsk->thread.regs->msr & MSR_SPE)
next prev parent reply other threads:[~2016-01-15 6:08 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-15 5:04 [PATCH V2 0/8] FP/VEC/VSX switching optimisations Cyril Bur
2016-01-15 5:04 ` [PATCH V2 1/8] selftests/powerpc: Test the preservation of FPU and VMX regs across syscall Cyril Bur
2016-01-15 5:04 ` [PATCH V2 2/8] selftests/powerpc: Test preservation of FPU and VMX regs across preemption Cyril Bur
2016-01-15 5:04 ` [PATCH V2 3/8] selftests/powerpc: Test FPU and VMX regs in signal ucontext Cyril Bur
2016-01-15 5:04 ` [PATCH V2 4/8] powerpc: Explicitly disable math features when copying thread Cyril Bur
2016-01-15 5:42 ` Michael Neuling
2016-01-15 5:54 ` Cyril Bur
2016-01-15 6:04 ` Michael Neuling
2016-01-15 5:04 ` [PATCH V2 5/8] powerpc: Restore FPU/VEC/VSX if previously used Cyril Bur
2016-01-15 6:02 ` Michael Neuling
2016-01-18 2:05 ` Cyril Bur
2016-01-15 5:04 ` [PATCH V2 6/8] powerpc: Add the ability to save FPU without giving it up Cyril Bur
2016-01-15 6:08 ` Michael Neuling [this message]
2016-01-15 7:38 ` Denis Kirjanov
2016-01-15 7:42 ` Denis Kirjanov
2016-01-15 5:04 ` [PATCH V2 7/8] powerpc: Add the ability to save Altivec " Cyril Bur
2016-01-15 5:04 ` [PATCH V2 8/8] powerpc: Add the ability to save VSX " Cyril Bur
2016-01-15 6:25 ` Michael Neuling
2016-01-18 2:10 ` Cyril Bur
2016-01-18 4:29 ` Michael Neuling
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