Re: [RFC PATCH 5/6] crypto: aesni-intel - Add bulk request support

[Eric Biggers <ebiggers3@gmail.com>]

On Thu, Jan 12, 2017 at 01:59:57PM +0100, Ondrej Mosnacek wrote:
> This patch implements bulk request handling in the AES-NI crypto drivers.
> The major advantage of this is that with bulk requests, the kernel_fpu_*
> functions (which are usually quite slow) are now called only once for the whole
> request.
> 

Hi Ondrej,

To what extent does the performance benefit of this patchset result from just
the reduced numbers of calls to kernel_fpu_begin() and kernel_fpu_end()?

If it's most of the benefit, would it make any sense to optimize
kernel_fpu_begin() and kernel_fpu_end() instead?

And if there are other examples besides kernel_fpu_begin/kernel_fpu_end where
the bulk API would provide a significant performance boost, can you mention
them?

Interestingly, the arm64 equivalent to kernel_fpu_begin()
(kernel_neon_begin_partial() in arch/arm64/kernel/fpsimd.c) appears to have an
optimization where the SIMD registers aren't saved if they were already saved.
I wonder why something similar isn't done on x86.

Eric