From: Shawn Landden <slandden@gmail.com>
To: linux-rt-users@vger.kernel.org, peterz@infradead.org,
wireguard@lists.zx2c4.com
Subject: Allowing SIMD in kernel mode without disabling preemption
Date: Sat, 18 May 2019 11:27:34 -0500 [thread overview]
Message-ID: <CA+49okpOX5-N33BLPEEeBTW4Wcn7sBWog7cBNT=ENLvOZ_MKVQ@mail.gmail.com> (raw)
I ported the x86 approach to allowing SIMD in kernel mode, even in an
interrupt, to powerpc[1], but I couldn't help wonder if it would be
possible without disabling preemption.
The scheduler just has to check the per-cpu in_kernel_fpu, and if it
is set, save the fpu state of the kernel thread, similar to what is
done for user-space threads with use_mode().
This way WireGuard would be fast even on preempt-rt kernels (it
currently turns off SIMD on them). Other crypto in the kernel is
woorse, and just unconditionally turns off preempt for each block of
data (look at arch/x86/crypto/chacha_glue.c ). Note that
kernel_fpu_begin() disables preemption, but I don't believe it has to.
Is there any complications with this approach that I am missing?
-Shawn Landden
[1] https://lists.ozlabs.org/pipermail/linuxppc-dev/2019-May/190704.html
reply other threads:[~2019-05-18 16:27 UTC|newest]
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