Messages in this thread Patch in this message | | | Date | Thu, 15 Jan 2015 21:27:09 -0500 | From | Rik van Riel <> | Subject | Re: [PATCH 2/3] x86, fpu: don't abuse ->has_fpu in __kernel_fpu_{begin,end}() |
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On 01/15/2015 02:20 PM, Oleg Nesterov wrote: > Now that we have in_kernel_fpu we can remove > __thread_clear_has_fpu() in __kernel_fpu_begin(). And this allows > to replace the asymmetrical and nontrivial use_eager_fpu + > tsk_used_math check in kernel_fpu_end() with the same > __thread_has_fpu() check. > > The logic becomes really simple; if _begin() does save() then > _end() needs restore(), this is controlled by __thread_has_fpu(). > Otherwise they do clts/stts unless use_eager_fpu(). > > Not only this makes begin/end symmetrical and imo more > understandable, potentially this allows to change irq_fpu_usable() > to avoid all other checks except "in_kernel_fpu". > > Also, with this patch __kernel_fpu_end() does > restore_fpu_checking() and WARNs if it fails instead of > math_state_restore(). I think this looks better because we no > longer need __thread_fpu_begin(), and it would be better to report > the failure in this case. > > Signed-off-by: Oleg Nesterov <oleg@redhat.com> --- > arch/x86/kernel/i387.c | 19 ++++++------------- 1 files changed, > 6 insertions(+), 13 deletions(-) > > diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c index > a815723..12088a3 100644 --- a/arch/x86/kernel/i387.c +++ > b/arch/x86/kernel/i387.c @@ -81,9 +81,7 @@ void > __kernel_fpu_begin(void) this_cpu_write(in_kernel_fpu, true); > > if (__thread_has_fpu(me)) { - __thread_clear_has_fpu(me);
I will put that line back in the patch series that defers the loading of FPU state until the switch to user space, but I guess we can go either way for now...
> __save_init_fpu(me); - /* We do 'stts()' in __kernel_fpu_end() */ > } else if (!use_eager_fpu()) { this_cpu_write(fpu_owner_task, > NULL); clts(); @@ -93,17 +91,12 @@ > EXPORT_SYMBOL(__kernel_fpu_begin); > > void __kernel_fpu_end(void) { - if (use_eager_fpu()) { - /* - * > For eager fpu, most the time, tsk_used_math() is true. - * > Restore the user math as we are done with the kernel usage. - * > At few instances during thread exit, signal handling etc, - * > tsk_used_math() is false. Those few places will take proper - * > actions, so we don't need to restore the math here. - */ - if > (likely(tsk_used_math(current))) - math_state_restore(); - } else > { + struct task_struct *me = current; + + if (__thread_has_fpu(me)) > { + if (WARN_ON(restore_fpu_checking(me))) + drop_init_fpu(me); > + } else if (!use_eager_fpu()) { stts(); } > >
- -- All rights reversed -----BEGIN PGP SIGNATURE----- Version: GnuPG v1
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