[PATCH v4 0/6] x86: Cleanups around slow_down_io()

[PATCH v4 0/6] 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

Changes in V3:
- rebase to tip/master kernel branch

Changes in V4:
- add patch 1 as prereq patch to the series

Juergen Gross (6):
  x86/irqflags: Fix build failure
  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             | 19 ++++---
 arch/x86/include/asm/irqflags.h       |  6 +-
 arch/x86/include/asm/paravirt-base.h  |  6 ++
 arch/x86/include/asm/paravirt.h       | 11 ----
 arch/x86/include/asm/paravirt_types.h |  2 -
 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 -
 16 files changed, 63 insertions(+), 159 deletions(-)

-- 
2.52.0

[PATCH v4 2/6] 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>
---
V3:
- rebase to tip/master kernel branch
---
 arch/x86/include/asm/io.h             |  9 ++++++---
 arch/x86/include/asm/paravirt-base.h  |  6 ++++++
 arch/x86/include/asm/paravirt.h       | 11 -----------
 arch/x86/include/asm/paravirt_types.h |  2 --
 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 +-----
 8 files changed, 16 insertions(+), 31 deletions(-)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index ca309a3227c7..8a9292ce7d2d 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -243,11 +243,16 @@ extern int io_delay_type;
 extern void io_delay_init(void);
 
 #if defined(CONFIG_PARAVIRT)
-#include <asm/paravirt.h>
+#include <asm/paravirt-base.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-base.h b/arch/x86/include/asm/paravirt-base.h
index 982a0b93bc76..3b9e7772d196 100644
--- a/arch/x86/include/asm/paravirt-base.h
+++ b/arch/x86/include/asm/paravirt-base.h
@@ -15,6 +15,8 @@ struct pv_info {
 #ifdef CONFIG_PARAVIRT_XXL
 	u16 extra_user_64bit_cs;  /* __USER_CS if none */
 #endif
+	bool io_delay;
+
 	const char *name;
 };
 
@@ -26,6 +28,10 @@ u64 _paravirt_ident_64(u64);
 #endif
 #define paravirt_nop	((void *)nop_func)
 
+#ifdef CONFIG_PARAVIRT
+#define call_io_delay() pv_info.io_delay
+#endif
+
 #ifdef CONFIG_PARAVIRT_SPINLOCKS
 void paravirt_set_cap(void);
 #else
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index b21072af731d..f4885bd98a18 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -19,17 +19,6 @@
 #include <linux/cpumask.h>
 #include <asm/frame.h>
 
-/* The paravirtualized I/O functions */
-static inline void slow_down_io(void)
-{
-	PVOP_VCALL0(pv_ops, cpu.io_delay);
-#ifdef REALLY_SLOW_IO
-	PVOP_VCALL0(pv_ops, cpu.io_delay);
-	PVOP_VCALL0(pv_ops, cpu.io_delay);
-	PVOP_VCALL0(pv_ops, cpu.io_delay);
-#endif
-}
-
 void native_flush_tlb_local(void);
 void native_flush_tlb_global(void);
 void native_flush_tlb_one_user(unsigned long addr);
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 7ccd41628d36..3946d0f69921 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -30,8 +30,6 @@ 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 a3e6936839b1..eee0d1a48802 100644
--- a/arch/x86/kernel/cpu/vmware.c
+++ b/arch/x86/kernel/cpu/vmware.c
@@ -339,7 +339,7 @@ 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 26ab6f8e36df..911950c9110c 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -75,12 +75,6 @@ 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)
@@ -327,7 +321,7 @@ 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 a6ed52cae003..792fa96b3233 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -94,6 +94,7 @@ struct pv_info pv_info = {
 #ifdef CONFIG_PARAVIRT_XXL
 	.extra_user_64bit_cs = __USER_CS,
 #endif
+	.io_delay = true,
 };
 
 /* 64-bit pagetable entries */
@@ -101,8 +102,6 @@ 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 8a19a88190ee..9c9695f5d158 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",
 };
 
@@ -1392,7 +1389,6 @@ asmlinkage __visible void __init xen_start_kernel(struct start_info *si)
 	pv_ops.cpu.invalidate_io_bitmap = xen_invalidate_io_bitmap;
 	pv_ops.cpu.update_io_bitmap = xen_update_io_bitmap;
 #endif
-	pv_ops.cpu.io_delay = xen_io_delay;
 	pv_ops.cpu.start_context_switch = xen_start_context_switch;
 	pv_ops.cpu.end_context_switch = xen_end_context_switch;
 
-- 
2.52.0

Re: [PATCH v4 0/6] x86: Cleanups around slow_down_io()

[Juergen Gross]

[-- Attachment #1.1.1: Type: text/plain, Size: 2156 bytes --]

Ping?

On 19.01.26 19:26, 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
> 
> Changes in V3:
> - rebase to tip/master kernel branch
> 
> Changes in V4:
> - add patch 1 as prereq patch to the series
> 
> Juergen Gross (6):
>    x86/irqflags: Fix build failure
>    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             | 19 ++++---
>   arch/x86/include/asm/irqflags.h       |  6 +-
>   arch/x86/include/asm/paravirt-base.h  |  6 ++
>   arch/x86/include/asm/paravirt.h       | 11 ----
>   arch/x86/include/asm/paravirt_types.h |  2 -
>   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 -
>   16 files changed, 63 insertions(+), 159 deletions(-)
> 


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Re: [PATCH v4 0/6] x86: Cleanups around slow_down_io()

[Juergen Gross]

[-- Attachment #1.1.1: Type: text/plain, Size: 2195 bytes --]

PING?

Now 3 weeks without any reaction...

On 19.01.26 19:26, 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
> 
> Changes in V3:
> - rebase to tip/master kernel branch
> 
> Changes in V4:
> - add patch 1 as prereq patch to the series
> 
> Juergen Gross (6):
>    x86/irqflags: Fix build failure
>    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             | 19 ++++---
>   arch/x86/include/asm/irqflags.h       |  6 +-
>   arch/x86/include/asm/paravirt-base.h  |  6 ++
>   arch/x86/include/asm/paravirt.h       | 11 ----
>   arch/x86/include/asm/paravirt_types.h |  2 -
>   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 -
>   16 files changed, 63 insertions(+), 159 deletions(-)
> 


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Re: [PATCH v4 0/6] x86: Cleanups around slow_down_io()

[Borislav Petkov]

On Mon, Feb 09, 2026 at 10:11:49AM +0100, Juergen Gross wrote:
> PING?
> 
> Now 3 weeks without any reaction...

Jürgen, there are other patchsets that need review too. And we have merge
window right now so no reviewing anyway.

And you know all that damn well!

How about you help us out and you start reviewing x86 patches instead of
pinging every week?

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v4 0/6] x86: Cleanups around slow_down_io()

[Juergen Gross]

[-- Attachment #1.1.1: Type: text/plain, Size: 2175 bytes --]

On 19.01.26 19:26, 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
> 
> Changes in V3:
> - rebase to tip/master kernel branch
> 
> Changes in V4:
> - add patch 1 as prereq patch to the series
> 
> Juergen Gross (6):
>    x86/irqflags: Fix build failure
>    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             | 19 ++++---
>   arch/x86/include/asm/irqflags.h       |  6 +-
>   arch/x86/include/asm/paravirt-base.h  |  6 ++
>   arch/x86/include/asm/paravirt.h       | 11 ----
>   arch/x86/include/asm/paravirt_types.h |  2 -
>   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 -
>   16 files changed, 63 insertions(+), 159 deletions(-)
> 

Any comments?


Juergen

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