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66 lines
2.1 KiB
Diff
66 lines
2.1 KiB
Diff
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Date: Thu, 30 Nov 2017 13:40:10 +0100
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Subject: [PATCH] crypto: limit more FPU-enabled sections
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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Those crypto drivers use SSE/AVX/… for their crypto work and in order to
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do so in kernel they need to enable the "FPU" in kernel mode which
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disables preemption.
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There are two problems with the way they are used:
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- the while loop which processes X bytes may create latency spikes and
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should be avoided or limited.
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- the cipher-walk-next part may allocate/free memory and may use
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kmap_atomic().
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The whole kernel_fpu_begin()/end() processing isn't probably that cheap.
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It most likely makes sense to process as much of those as possible in one
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go. The new *_fpu_sched_rt() schedules only if a RT task is pending.
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Probably we should measure the performance those ciphers in pure SW
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mode and with this optimisations to see if it makes sense to keep them
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for RT.
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This kernel_fpu_resched() makes the code more preemptible which might hurt
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performance.
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Cc: stable-rt@vger.kernel.org
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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arch/x86/include/asm/fpu/api.h | 1 +
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arch/x86/kernel/fpu/core.c | 12 ++++++++++++
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2 files changed, 13 insertions(+)
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--- a/arch/x86/include/asm/fpu/api.h
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+++ b/arch/x86/include/asm/fpu/api.h
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@@ -28,6 +28,7 @@ extern void kernel_fpu_begin_mask(unsign
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extern void kernel_fpu_end(void);
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extern bool irq_fpu_usable(void);
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extern void fpregs_mark_activate(void);
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+extern void kernel_fpu_resched(void);
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/* Code that is unaware of kernel_fpu_begin_mask() can use this */
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static inline void kernel_fpu_begin(void)
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--- a/arch/x86/kernel/fpu/core.c
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+++ b/arch/x86/kernel/fpu/core.c
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@@ -159,6 +159,18 @@ void kernel_fpu_end(void)
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}
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EXPORT_SYMBOL_GPL(kernel_fpu_end);
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+void kernel_fpu_resched(void)
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+{
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+ WARN_ON_FPU(!this_cpu_read(in_kernel_fpu));
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+
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+ if (should_resched(PREEMPT_OFFSET)) {
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+ kernel_fpu_end();
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+ cond_resched();
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+ kernel_fpu_begin();
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+ }
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+}
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+EXPORT_SYMBOL_GPL(kernel_fpu_resched);
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+
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/*
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* Save the FPU state (mark it for reload if necessary):
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*
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