Re: [PATCH net-next v9 01/19] asm: simd context helper API

[Thomas Gleixner <tglx@linutronix.de>]

Jason,

On Fri, 22 Mar 2019, Jason A. Donenfeld wrote:
> index 000000000000..264ed84b41d8
> --- /dev/null
> +++ b/arch/arm/include/asm/simd.h
> @@ -0,0 +1,63 @@
> +/* SPDX-License-Identifier: GPL-2.0

The SPDX identifier has to be in a separate comment line.

/* SPDX-License-Identifier: GPL-2.0 */
/*
 * Copyright (C) 2015-2018 Jason....
 */

Yes, it looks odd, but it's defined that way.

> +static __must_check inline bool simd_use(simd_context_t *ctx)
> +{
> +	if (!(*ctx & HAVE_FULL_SIMD))
> +		return false;
> +	if (*ctx & HAVE_SIMD_IN_USE)
> +		return true;
> +	kernel_neon_begin();
> +	*ctx |= HAVE_SIMD_IN_USE;
> +	return true;
> +}

> +static __must_check inline bool simd_use(simd_context_t *ctx)
> +{
> +	if (!(*ctx & HAVE_FULL_SIMD))
> +		return false;
> +	if (*ctx & HAVE_SIMD_IN_USE)
> +		return true;
> +	kernel_neon_begin();
> +	*ctx |= HAVE_SIMD_IN_USE;
> +	return true;
> +}

> +static __must_check inline bool simd_use(simd_context_t *ctx)
> +{
> +#if !defined(CONFIG_UML)
> +	if (!(*ctx & HAVE_FULL_SIMD))
> +		return false;
> +	if (*ctx & HAVE_SIMD_IN_USE)
> +		return true;
> +	kernel_fpu_begin();
> +	*ctx |= HAVE_SIMD_IN_USE;
> +	return true;
> +#else
> +	return false;
> +#endif
> +}

So now we have 3 almost identical copies of the same thing and x86/UM
handling it differently than the ARM(64) ones.

That can be completely avoided. Untested patch below.

Thanks,

	tglx

8<-------------
--- /dev/null
+++ b/arch/arm/include/asm/simd.h
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2015-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ */
+#ifndef _ASM_SIMD_H
+#define _ASM_SIMD_H
+
+#ifdef CONFIG_KERNEL_MODE_NEON
+#include <asm/neon.h>
+
+static __must_check inline bool may_use_simd(void)
+{
+	return !in_nmi() && !in_irq() && !in_serving_softirq();
+}
+
+static inline void arch_simd_end(void)
+{
+	kernel_neon_end();
+}
+
+static inline void arch_simd_begin(void)
+{
+	kernel_neon_begin();
+}
+
+#else
+#include <asm-generic/simd.h>
+#endif
+
+#endif /* _ASM_SIMD_H */
--- a/arch/arm64/include/asm/simd.h
+++ b/arch/arm64/include/asm/simd.h
@@ -1,11 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * Copyright (C) 2017 Linaro Ltd. <ard.biesheuvel@linaro.org>
- *
- * This program is free software; you can redistribute it and/or modify it
- * under the terms of the GNU General Public License version 2 as published
- * by the Free Software Foundation.
+ * Copyright (C) 2015-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
  */
 
+#include <linux/simd.h>
 #ifndef __ASM_SIMD_H
 #define __ASM_SIMD_H
 
@@ -16,6 +15,8 @@
 #include <linux/types.h>
 
 #ifdef CONFIG_KERNEL_MODE_NEON
+#include <asm/neon.h>
+#include <asm/simd.h>
 
 DECLARE_PER_CPU(bool, kernel_neon_busy);
 
@@ -40,12 +41,18 @@ static __must_check inline bool may_use_
 		!this_cpu_read(kernel_neon_busy);
 }
 
-#else /* ! CONFIG_KERNEL_MODE_NEON */
+static inline void arch_simd_end(void)
+{
+	kernel_neon_end();
+}
 
-static __must_check inline bool may_use_simd(void) {
-	return false;
+static inline void arch_simd_begin(void)
+{
+	kernel_neon_begin();
 }
 
-#endif /* ! CONFIG_KERNEL_MODE_NEON */
+#else
+#include <asm-generic/simd.h>
+#endif
 
 #endif
--- a/arch/x86/include/asm/simd.h
+++ b/arch/x86/include/asm/simd.h
@@ -1,4 +1,12 @@
 /* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2015-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ */
+
+#ifndef _ASM_SIMD_H
+#define _ASM_SIMD_H
+
+#ifndef CONFIG_UML
 
 #include <asm/fpu/api.h>
 
@@ -10,3 +18,21 @@ static __must_check inline bool may_use_
 {
 	return irq_fpu_usable();
 }
+
+static inline void arch_simd_begin(void)
+{
+	kernel_fpu_begin();
+}
+
+static inline void arch_simd_end(void)
+{
+	kernel_fpu_end();
+}
+
+#else
+#include <asm-generic/simd.h>
+#endif
+
+#include <linux/simd.h>
+
+#endif /* _ASM_SIMD_H */
--- a/include/asm-generic/simd.h
+++ b/include/asm-generic/simd.h
@@ -1,7 +1,12 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 
+#ifndef _ASM_SIMD_H
+#define _ASM_SIMD_H
+
 #include <linux/hardirq.h>
 
+#define SIMD_GENERIC	1
+
 /*
  * may_use_simd - whether it is allowable at this time to issue SIMD
  *                instructions or access the SIMD register file
@@ -13,3 +18,10 @@ static __must_check inline bool may_use_
 {
 	return !in_interrupt();
 }
+
+static inline void arch_simd_begin(void) { }
+static inline void arch_simd_end(void) { }
+
+#include <linux/simd.h>
+
+#endif /* _ASM_SIMD_H */
--- /dev/null
+++ b/include/linux/simd.h
@@ -0,0 +1,82 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2015-2018 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
+ */
+
+#ifndef _SIMD_H
+#define _SIMD_H
+
+typedef enum {
+	HAVE_NO_SIMD		= 1 << 0,
+	HAVE_FULL_SIMD		= 1 << 1,
+	HAVE_SIMD_IN_USE	= 1 << 31
+} simd_context_t;
+
+#define DONT_USE_SIMD ((simd_context_t []){ HAVE_NO_SIMD })
+
+#include <asm/simd.h>
+
+#ifndef SIMD_GENERIC
+
+#include <linux/sched.h>
+
+static inline bool simd_relax(simd_context_t *ctx)
+{
+#ifdef CONFIG_PREEMPT
+	if ((*ctx & HAVE_SIMD_IN_USE) && need_resched()) {
+		simd_put(ctx);
+		simd_get(ctx);
+		return true;
+	}
+#endif
+	return false;
+}
+
+static inline void simd_get(simd_context_t *ctx)
+{
+	*ctx = may_use_simd() ? HAVE_FULL_SIMD : HAVE_NO_SIMD;
+}
+
+static inline void simd_put(simd_context_t *ctx)
+{
+	if (*ctx & HAVE_SIMD_IN_USE)
+		arch_simd_end();
+
+	*ctx = HAVE_NO_SIMD;
+}
+
+static __must_check inline bool simd_use(simd_context_t *ctx)
+{
+	if (!(*ctx & HAVE_FULL_SIMD))
+		return false;
+	if (*ctx & HAVE_SIMD_IN_USE)
+		return true;
+	arch_simd_begin();
+	*ctx |= HAVE_SIMD_IN_USE;
+	return true;
+}
+
+#else /* !SIMD_GENERIC */
+
+static inline bool simd_relax(simd_context_t *ctx)
+{
+	return false;
+}
+
+static inline void simd_get(simd_context_t *ctx)
+{
+	*ctx = HAVE_NO_SIMD;
+}
+
+static inline void simd_put(simd_context_t *ctx)
+{
+}
+
+static __must_check inline bool simd_use(simd_context_t *ctx)
+{
+	return false;
+}
+
+#endif /* SIMD_GENERIC */
+
+#endif /* _SIMD_H */