[PATCH v2 0/5] x86: Cleanups around slow_down_io()

[PATCH v2 0/5] x86: Cleanups around slow_down_io()

[Juergen Gross]

While looking at paravirt cleanups I stumbled over slow_down_io() and
the related REALLY_SLOW_IO define.

Do several cleanups, resulting in a deletion of REALLY_SLOW_IO and the
io_delay() paravirt function hook.

Patch 4 is removing the config options for selecting the default delay
mechanism and sets the default to "no delay". This is in preparation of
removing the io_delay() functionality completely, as suggested by Ingo
Molnar.

Patch 5 is adding an additional config option allowing to avoid
building io_delay.c (default is still to build it).

Changes in V2:
- patches 2 and 3 of V1 have been applied
- new patches 4 and 5

Juergen Gross (5):
  x86/paravirt: Replace io_delay() hook with a bool
  block/floppy: Don't use REALLY_SLOW_IO for delays
  x86/io: Remove REALLY_SLOW_IO handling
  x86/io_delay: Switch io_delay() default mechanism to "none"
  x86/io_delay: Add config option for controlling build of io_delay.

 arch/x86/Kconfig                      |  8 +++
 arch/x86/Kconfig.debug                | 30 ----------
 arch/x86/include/asm/floppy.h         | 31 ++++++++--
 arch/x86/include/asm/io.h             | 17 +++---
 arch/x86/include/asm/paravirt.h       | 11 +---
 arch/x86/include/asm/paravirt_types.h |  3 +-
 arch/x86/kernel/Makefile              |  3 +-
 arch/x86/kernel/cpu/vmware.c          |  2 +-
 arch/x86/kernel/io_delay.c            | 81 +--------------------------
 arch/x86/kernel/kvm.c                 |  8 +--
 arch/x86/kernel/paravirt.c            |  3 +-
 arch/x86/kernel/setup.c               |  4 +-
 arch/x86/xen/enlighten_pv.c           |  6 +-
 drivers/block/floppy.c                |  2 -
 14 files changed, 55 insertions(+), 154 deletions(-)

-- 
2.51.0

[PATCH v2 1/5] x86/paravirt: Replace io_delay() hook with a bool

[Juergen Gross]

The io_delay() paravirt hook is in no way performance critical and all
users setting it to a different function than native_io_delay() are
using an empty function as replacement.

This enables to replace the hook with a bool indicating whether
native_io_delay() should be called.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 arch/x86/include/asm/io.h             |  7 +++++--
 arch/x86/include/asm/paravirt.h       | 11 +----------
 arch/x86/include/asm/paravirt_types.h |  3 +--
 arch/x86/kernel/cpu/vmware.c          |  2 +-
 arch/x86/kernel/kvm.c                 |  8 +-------
 arch/x86/kernel/paravirt.c            |  3 +--
 arch/x86/xen/enlighten_pv.c           |  6 +-----
 7 files changed, 11 insertions(+), 29 deletions(-)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index ca309a3227c7..0448575569b9 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -245,9 +245,14 @@ extern void io_delay_init(void);
 #if defined(CONFIG_PARAVIRT)
 #include <asm/paravirt.h>
 #else
+#define call_io_delay() true
+#endif
 
 static inline void slow_down_io(void)
 {
+	if (!call_io_delay())
+		return;
+
 	native_io_delay();
 #ifdef REALLY_SLOW_IO
 	native_io_delay();
@@ -256,8 +261,6 @@ static inline void slow_down_io(void)
 #endif
 }
 
-#endif
-
 #define BUILDIO(bwl, type)						\
 static inline void out##bwl##_p(type value, u16 port)			\
 {									\
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index b5e59a7ba0d0..0ab798d234cc 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -53,16 +53,7 @@ static inline u64 paravirt_steal_clock(int cpu)
 void __init paravirt_set_cap(void);
 #endif
 
-/* The paravirtualized I/O functions */
-static inline void slow_down_io(void)
-{
-	PVOP_VCALL0(cpu.io_delay);
-#ifdef REALLY_SLOW_IO
-	PVOP_VCALL0(cpu.io_delay);
-	PVOP_VCALL0(cpu.io_delay);
-	PVOP_VCALL0(cpu.io_delay);
-#endif
-}
+#define call_io_delay() pv_info.io_delay
 
 void native_flush_tlb_local(void);
 void native_flush_tlb_global(void);
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 3502939415ad..b4c15856eab5 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -36,6 +36,7 @@ struct pv_info {
 #ifdef CONFIG_PARAVIRT_XXL
 	u16 extra_user_64bit_cs;  /* __USER_CS if none */
 #endif
+	bool io_delay;
 
 	const char *name;
 };
@@ -51,8 +52,6 @@ struct pv_lazy_ops {
 
 struct pv_cpu_ops {
 	/* hooks for various privileged instructions */
-	void (*io_delay)(void);
-
 #ifdef CONFIG_PARAVIRT_XXL
 	unsigned long (*get_debugreg)(int regno);
 	void (*set_debugreg)(int regno, unsigned long value);
diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c
index cb3f900c46fc..47db25d63c8d 100644
--- a/arch/x86/kernel/cpu/vmware.c
+++ b/arch/x86/kernel/cpu/vmware.c
@@ -338,7 +338,7 @@ arch_initcall(activate_jump_labels);
 static void __init vmware_paravirt_ops_setup(void)
 {
 	pv_info.name = "VMware hypervisor";
-	pv_ops.cpu.io_delay = paravirt_nop;
+	pv_info.io_delay = false;
 
 	if (vmware_tsc_khz == 0)
 		return;
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index df78ddee0abb..24e403cdce69 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -74,12 +74,6 @@ DEFINE_PER_CPU_DECRYPTED(struct kvm_steal_time, steal_time) __aligned(64) __visi
 static int has_steal_clock = 0;
 
 static int has_guest_poll = 0;
-/*
- * No need for any "IO delay" on KVM
- */
-static void kvm_io_delay(void)
-{
-}
 
 #define KVM_TASK_SLEEP_HASHBITS 8
 #define KVM_TASK_SLEEP_HASHSIZE (1<<KVM_TASK_SLEEP_HASHBITS)
@@ -313,7 +307,7 @@ static void __init paravirt_ops_setup(void)
 	pv_info.name = "KVM";
 
 	if (kvm_para_has_feature(KVM_FEATURE_NOP_IO_DELAY))
-		pv_ops.cpu.io_delay = kvm_io_delay;
+		pv_info.io_delay = false;
 
 #ifdef CONFIG_X86_IO_APIC
 	no_timer_check = 1;
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index ab3e172dcc69..8ee952e7e7d4 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -113,6 +113,7 @@ struct pv_info pv_info = {
 #ifdef CONFIG_PARAVIRT_XXL
 	.extra_user_64bit_cs = __USER_CS,
 #endif
+	.io_delay = true,
 };
 
 /* 64-bit pagetable entries */
@@ -120,8 +121,6 @@ struct pv_info pv_info = {
 
 struct paravirt_patch_template pv_ops = {
 	/* Cpu ops. */
-	.cpu.io_delay		= native_io_delay,
-
 #ifdef CONFIG_PARAVIRT_XXL
 	.cpu.cpuid		= native_cpuid,
 	.cpu.get_debugreg	= pv_native_get_debugreg,
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 4806cc28d7ca..a43b525f25cd 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1046,10 +1046,6 @@ static void xen_update_io_bitmap(void)
 }
 #endif
 
-static void xen_io_delay(void)
-{
-}
-
 static DEFINE_PER_CPU(unsigned long, xen_cr0_value);
 
 static unsigned long xen_read_cr0(void)
@@ -1209,6 +1205,7 @@ void __init xen_setup_vcpu_info_placement(void)
 
 static const struct pv_info xen_info __initconst = {
 	.extra_user_64bit_cs = FLAT_USER_CS64,
+	.io_delay = false,
 	.name = "Xen",
 };
 
@@ -1253,7 +1250,6 @@ static const typeof(pv_ops) xen_cpu_ops __initconst = {
 		.invalidate_io_bitmap = xen_invalidate_io_bitmap,
 		.update_io_bitmap = xen_update_io_bitmap,
 #endif
-		.io_delay = xen_io_delay,
 
 		.start_context_switch = xen_start_context_switch,
 		.end_context_switch = xen_end_context_switch,
-- 
2.51.0

Re: [PATCH v2 0/5] x86: Cleanups around slow_down_io()

[Juergen Gross]

[-- Attachment #1.1.1: Type: text/plain, Size: 1892 bytes --]

Gentle ping.

On 16.12.25 14:41, Juergen Gross wrote:
> While looking at paravirt cleanups I stumbled over slow_down_io() and
> the related REALLY_SLOW_IO define.
> 
> Do several cleanups, resulting in a deletion of REALLY_SLOW_IO and the
> io_delay() paravirt function hook.
> 
> Patch 4 is removing the config options for selecting the default delay
> mechanism and sets the default to "no delay". This is in preparation of
> removing the io_delay() functionality completely, as suggested by Ingo
> Molnar.
> 
> Patch 5 is adding an additional config option allowing to avoid
> building io_delay.c (default is still to build it).
> 
> Changes in V2:
> - patches 2 and 3 of V1 have been applied
> - new patches 4 and 5
> 
> Juergen Gross (5):
>    x86/paravirt: Replace io_delay() hook with a bool
>    block/floppy: Don't use REALLY_SLOW_IO for delays
>    x86/io: Remove REALLY_SLOW_IO handling
>    x86/io_delay: Switch io_delay() default mechanism to "none"
>    x86/io_delay: Add config option for controlling build of io_delay.
> 
>   arch/x86/Kconfig                      |  8 +++
>   arch/x86/Kconfig.debug                | 30 ----------
>   arch/x86/include/asm/floppy.h         | 31 ++++++++--
>   arch/x86/include/asm/io.h             | 17 +++---
>   arch/x86/include/asm/paravirt.h       | 11 +---
>   arch/x86/include/asm/paravirt_types.h |  3 +-
>   arch/x86/kernel/Makefile              |  3 +-
>   arch/x86/kernel/cpu/vmware.c          |  2 +-
>   arch/x86/kernel/io_delay.c            | 81 +--------------------------
>   arch/x86/kernel/kvm.c                 |  8 +--
>   arch/x86/kernel/paravirt.c            |  3 +-
>   arch/x86/kernel/setup.c               |  4 +-
>   arch/x86/xen/enlighten_pv.c           |  6 +-
>   drivers/block/floppy.c                |  2 -
>   14 files changed, 55 insertions(+), 154 deletions(-)
> 


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