Hello,
In order to do fast crypto, people like to use vector instructions,
which make use of the FPU registers. Typically things resemble this
pattern:
kernel_fpu_begin();
encrypt();
kernel_fpu_end();
If there are multiple things to encrypt, one pattern is:
for (thing) {
kernel_fpu_begin();
encrypt(thing);
kernel_fpu_end();
}
But it turns out this is slow, so instead it's better to:
kernel_fpu_begin();
for (thing)
encrypt(thing);
kernel_fpu_end();
However, what if that innerloop has some spinlocks?
kernel_fpu_begin();
for (thing) {
encrypt(thing);
spin_lock(queue_lock);
add_to_queue(queue, thing);
spin_unlock(queue_lock);
}
kernel_fpu_end();
On normal kernels, that's certainly okay. But on rt kernels, spinlocks
call schedule(), and kernel_fpu_begin() explicitly disables
preemption, so everything explodes.
I'm wondering if -rt has any ideas about not having a strict
preemption requirement for kernel_fpu_begin/end, so that the ordinary
pattern can work on -rt kernels without exploding.
Regards,
Jason
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