Re: [RFC PATCH 03/11] x86,fpu: move __thread_fpu_begin to when the task has the fpu

Oleg Nesterov
2015-01-13T15:25:32Z

On 01/11, riel@redhat.com wrote:
>
> --- a/arch/x86/include/asm/fpu-internal.h
> +++ b/arch/x86/include/asm/fpu-internal.h
> @@ -420,7 +420,6 @@ static inline void switch_fpu_prepare(struct task_struct *old, struct task_struc
> if (preload) {
> new->thread.fpu_counter++;
> set_thread_flag(TIF_LOAD_FPU);
> - __thread_set_has_fpu(new);
> prefetch(new->thread.fpu.state);
> } else if (!use_eager_fpu())
> stts();
> @@ -436,7 +435,6 @@ static inline void switch_fpu_prepare(struct task_struct *old, struct task_struc
> prefetch(new->thread.fpu.state);
> set_thread_flag(TIF_LOAD_FPU);
> }
> - __thread_fpu_begin(new);
> }
> /* else: CR0.TS is still set from a previous FPU switch */
> }
> @@ -451,6 +449,7 @@ static inline void switch_fpu_prepare(struct task_struct *old, struct task_struc
> static inline void switch_fpu_finish(struct task_struct *new)
> {
> if (test_and_clear_thread_flag(TIF_LOAD_FPU)) {
> + __thread_fpu_begin(new);
> if (unlikely(restore_fpu_checking(new)))
> drop_init_fpu(new);
> }

Then perhaps it makes sense to move fpu_lazy_restore() to fpu_finish() too ?

Either way, afaics we do not need use_eager_fpu() before fpu_lazy_restore(),
and this reminds me that every use_eager_fpu() check in switch_fpu_prepare()
looks confusing.

Oleg.