percpu area using gs segment

This speeds up smp again, by storing the struct processor
in a percpu area and avoiding an expensive cpu_number every call
of current_processor(), as well as getting the cpu_number by
an offset into the percpu area.  Untested on 64 bit
and work remains to use other percpu arrays.

TESTED: (NCPUS=8) -smp 1 boots to login shell ~2x slower than uniprocessor
TESTED: (NCPUS=8) -smp 2 boots to INIT but hangs there
TESTED: (NCPUS=8) -smp 4 gets stuck seemingly within rumpdisk and hangs
TESTED: (NCPUS=1) uniprocessor is a bit faster than normal

Message-Id: <20230924103428.455966-3-damien@zamaudio.com>

13 files changed, 177 insertions, 31 deletions

diff --git a/i386/Makefrag.am b/i386/Makefrag.am
index 274e8695..c1724cea 100644
--- a/i386/Makefrag.am
+++ b/i386/Makefrag.am
@@ -108,6 +108,8 @@ libkernel_a_SOURCES += \
 	i386/i386/irq.c \
 	i386/i386/irq.h \
 	i386/i386/msr.h \
+	i386/i386/percpu.c \
+	i386/i386/percpu.h \
 	i386/i386/pit.c \
 	i386/i386/pit.h
 
diff --git a/i386/i386/cpu_number.h b/i386/i386/cpu_number.h
index 8357be84..6ba46e4b 100644
--- a/i386/i386/cpu_number.h
+++ b/i386/i386/cpu_number.h
@@ -30,6 +30,8 @@
 #ifndef	_I386_CPU_NUMBER_H_
 #define	_I386_CPU_NUMBER_H_
 
+#define MY(stm)		%gs:PERCPU_##stm
+
 #if	NCPUS > 1
 
 #ifdef __i386__
@@ -45,8 +47,8 @@
 	shrl	$24, reg		;\
 	movl	%cs:CX(cpu_id_lut, reg), reg	;\
 
-/* Never call CPU_NUMBER(%esi) */
-#define CPU_NUMBER(reg)		\
+/* Never call CPU_NUMBER_NO_GS(%esi) */
+#define CPU_NUMBER_NO_GS(reg)		\
 	pushl	%esi		;\
 	pushl	%eax		;\
 	pushl	%ebx		;\
@@ -63,20 +65,29 @@
 	movl	%esi, reg	;\
 	popl	%esi		;\
 
+#define CPU_NUMBER(reg)	\
+	movl    MY(CPU_ID), reg;
+
 #ifndef __ASSEMBLER__
 #include <kern/cpu_number.h>
 #include <i386/apic.h>
+#include <i386/percpu.h>
 
-static inline int cpu_number(void)
+static inline int cpu_number_slow(void)
 {
 	return cpu_id_lut[apic_get_current_cpu()];
 }
 
+static inline int cpu_number(void)
+{
+	return percpu_get(int, cpu_id);
+}
 #endif
 
 #else	/* NCPUS == 1 */
 
 #define	CPU_NUMBER_NO_STACK(reg)
+#define	CPU_NUMBER_NO_GS(reg)
 #define	CPU_NUMBER(reg)
 #define	CX(addr,reg)	addr
 
diff --git a/i386/i386/fpu.c b/i386/i386/fpu.c
index fefe5e49..e1818683 100644
--- a/i386/i386/fpu.c
+++ b/i386/i386/fpu.c
@@ -119,7 +119,7 @@ init_fpu(void)
 #else	/* MACH_RING1 */
 	unsigned int native = 0;
 
-	if (machine_slot[cpu_number()].cpu_type >= CPU_TYPE_I486)
+	if (machine_slot[cpu_number_slow()].cpu_type >= CPU_TYPE_I486)
 		native = CR0_NE;
 
 	/*
diff --git a/i386/i386/gdt.c b/i386/i386/gdt.c
index ddda603b..4edd3ec5 100644
--- a/i386/i386/gdt.c
+++ b/i386/i386/gdt.c
@@ -35,6 +35,8 @@
 
 #include <kern/assert.h>
 #include <intel/pmap.h>
+#include <kern/cpu_number.h>
+#include <machine/percpu.h>
 
 #include "vm_param.h"
 #include "seg.h"
@@ -48,7 +50,7 @@ extern
 struct real_descriptor gdt[GDTSZ];
 
 static void
-gdt_fill(struct real_descriptor *mygdt)
+gdt_fill(int cpu, struct real_descriptor *mygdt)
 {
 	/* Initialize the kernel code and data segment descriptors.  */
 #ifdef __x86_64__
@@ -73,6 +75,16 @@ gdt_fill(struct real_descriptor *mygdt)
 			    0xffffffff,
 			    ACC_PL_K|ACC_DATA_W, SZ_32);
 #endif	/* MACH_PV_DESCRIPTORS */
+	vm_offset_t thiscpu = kvtolin(&percpu_array[cpu]);
+	_fill_gdt_descriptor(mygdt, PERCPU_DS,
+			    thiscpu,
+			    thiscpu + sizeof(struct percpu) - 1,
+#ifdef __x86_64__
+			    ACC_PL_K|ACC_DATA_W, SZ_64
+#else
+			    ACC_PL_K|ACC_DATA_W, SZ_32
+#endif
+	);
 #endif
 
 #ifdef	MACH_PV_DESCRIPTORS
@@ -119,15 +131,16 @@ reload_segs(void)
 		     
 		     "movw	%w1,%%ds\n"
 		     "movw	%w1,%%es\n"
+		     "movw	%w3,%%gs\n"
 		     "movw	%w1,%%ss\n"
-		     : : "i" (KERNEL_CS), "r" (KERNEL_DS), "r" (0));
+		     : : "i" (KERNEL_CS), "r" (KERNEL_DS), "r" (0), "r" (PERCPU_DS));
 #endif
 }
 
 void
 gdt_init(void)
 {
-	gdt_fill(gdt);
+	gdt_fill(0, gdt);
 
 	reload_segs();
 
@@ -146,7 +159,7 @@ gdt_init(void)
 void
 ap_gdt_init(int cpu)
 {
-	gdt_fill(mp_gdt[cpu]);
+	gdt_fill(cpu, mp_gdt[cpu]);
 
 	reload_segs();
 }
diff --git a/i386/i386/gdt.h b/i386/i386/gdt.h
index 80ca8ada..c7da012a 100644
--- a/i386/i386/gdt.h
+++ b/i386/i386/gdt.h
@@ -77,11 +77,9 @@
 
 /*			0x58		   used by user TSS in 64bit mode */
 
-#ifdef __x86_64__
-#define	GDTSZ		sel_idx(0x60)
-#else
-#define	GDTSZ		sel_idx(0x58)
-#endif
+#define PERCPU_DS	0x68		/* per-cpu data mapping */
+
+#define	GDTSZ		sel_idx(0x70)
 
 #ifndef __ASSEMBLER__
 
diff --git a/i386/i386/i386asm.sym b/i386/i386/i386asm.sym
index 5d546c08..d96b8be8 100644
--- a/i386/i386/i386asm.sym
+++ b/i386/i386/i386asm.sym
@@ -53,6 +53,8 @@ expr	CALL_PMAP_UPDATE
 
 offset	ApicLocalUnit		lu	apic_id		APIC_ID
 
+offset	percpu			pc	cpu_id		PERCPU_CPU_ID
+
 offset	pcb			pcb	iss
 
 offset	thread			th	pcb
diff --git a/i386/i386/locore.S b/i386/i386/locore.S
index 0cac8df4..870db785 100644
--- a/i386/i386/locore.S
+++ b/i386/i386/locore.S
@@ -244,7 +244,7 @@ timer_normalize:
  * Switch to a new timer.
  */
 ENTRY(timer_switch)
-	CPU_NUMBER(%edx)			/* get this CPU  */
+	CPU_NUMBER_NO_GS(%edx)			/* get this CPU  */
 	movl	VA_ETC,%ecx			/* get timer */
 	movl	CX(EXT(current_tstamp),%edx),%eax	/* get old time stamp  */
 	movl	%ecx,CX(EXT(current_tstamp),%edx)	/* set new time stamp */
@@ -262,7 +262,7 @@ ENTRY(timer_switch)
  * Initialize the first timer for a CPU.
  */
 ENTRY(start_timer)
-	CPU_NUMBER(%edx)			/* get this CPU */
+	CPU_NUMBER_NO_GS(%edx)			/* get this CPU */
 	movl	VA_ETC,%ecx			/* get timer */
 	movl	%ecx,CX(EXT(current_tstamp),%edx)	/* set initial time stamp */
 	movl	S_ARG0,%ecx			/* get timer */
@@ -469,7 +469,8 @@ trap_push_segs:
 	mov	%ax,%ds			/* (same as kernel stack segment) */
 	mov	%ax,%es
 	mov	%ax,%fs
-	mov	%ax,%gs
+	mov	$(PERCPU_DS),%ax
+	movw	%ax,%gs
 
 trap_set_segs:
 	cld				/* clear direction flag */
@@ -673,7 +674,7 @@ ENTRY(all_intrs)
 	pushl	%edx
 	cld				/* clear direction flag */
 
-	CPU_NUMBER(%ecx)
+	CPU_NUMBER_NO_GS(%ecx)
 	movl	%esp,%edx		/* on an interrupt stack? */
 	and	$(~(INTSTACK_SIZE-1)),%edx
 	cmpl	%ss:CX(EXT(int_stack_base),%ecx),%edx
@@ -687,7 +688,8 @@ ENTRY(all_intrs)
 	mov	%dx,%ds
 	mov	%dx,%es
 	mov	%dx,%fs
-	mov	%dx,%gs
+	mov	$(PERCPU_DS),%dx
+	movw	%dx,%gs
 
 	CPU_NUMBER(%edx)
 
@@ -745,7 +747,7 @@ LEXT(return_to_iret)			/* to find the return from calling interrupt) */
 	iret				/* return to caller */
 
 int_from_intstack:
-	CPU_NUMBER(%edx)
+	CPU_NUMBER_NO_GS(%edx)
 	cmpl	CX(EXT(int_stack_base),%edx),%esp /* seemingly looping? */
 	jb	stack_overflowed	/* if not: */
 	call	EXT(interrupt)		/* call interrupt routine */
@@ -793,7 +795,8 @@ ast_from_interrupt:
 	mov	%dx,%ds
 	mov	%dx,%es
 	mov	%dx,%fs
-	mov	%dx,%gs
+	mov	$(PERCPU_DS),%dx
+	movw	%dx,%gs
 
 	CPU_NUMBER(%edx)
 	TIME_TRAP_UENTRY
@@ -1052,7 +1055,8 @@ syscall_entry_2:
 	mov	%dx,%ds
 	mov	%dx,%es
 	mov	%dx,%fs
-	mov	%dx,%gs
+	mov	$(PERCPU_DS),%dx
+	movw	%dx,%gs
 
 /*
  * Shuffle eflags,eip,cs into proper places
diff --git a/i386/i386/mp_desc.c b/i386/i386/mp_desc.c
index f1a1f989..f4ccc381 100644
--- a/i386/i386/mp_desc.c
+++ b/i386/i386/mp_desc.c
@@ -238,6 +238,7 @@ cpu_setup(int cpu)
     flush_instr_queue();
     printf("AP=(%u) paging done\n", cpu);
 
+    init_percpu(cpu);
     mp_desc_init(cpu);
     printf("AP=(%u) mpdesc done\n", cpu);
 
@@ -275,7 +276,7 @@ cpu_setup(int cpu)
 void
 cpu_ap_main()
 {
-    int cpu = cpu_number();
+    int cpu = cpu_number_slow();
 
     do {
 	cpu_pause();
diff --git a/i386/i386/percpu.c b/i386/i386/percpu.c
new file mode 100644
index 00000000..a4db7b68
--- /dev/null
+++ b/i386/i386/percpu.c
@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) 2023 Free Software Foundation, Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <i386/smp.h>
+#include <i386/apic.h>
+#include <kern/cpu_number.h>
+#include <i386/percpu.h>
+
+struct percpu percpu_array[NCPUS] = {0};
+
+void init_percpu(int cpu)
+{
+    int apic_id = apic_get_current_cpu();
+
+    percpu_array[cpu].self = &percpu_array[cpu];
+    percpu_array[cpu].apic_id = apic_id;
+    percpu_array[cpu].cpu_id = cpu;
+}
diff --git a/i386/i386/percpu.h b/i386/i386/percpu.h
new file mode 100644
index 00000000..202504da
--- /dev/null
+++ b/i386/i386/percpu.h
@@ -0,0 +1,83 @@
+/*
+ * Copyright (c) 2023 Free Software Foundation, Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef _PERCPU_H_
+#define _PERCPU_H_
+
+struct percpu;
+
+#define percpu_assign(stm, val)     \
+    asm("mov %[src], %%gs:%c[offs]" \
+         : /* No outputs */         \
+         : [src] "r" (val), [offs] "e" (__builtin_offsetof(struct percpu, stm)) \
+         : );
+
+#define percpu_get(typ, stm)        \
+MACRO_BEGIN                         \
+    typ val_;                       \
+                                    \
+    asm("mov %%gs:%c[offs], %[dst]" \
+         : [dst] "=r" (val_)        \
+         : [offs] "e" (__builtin_offsetof(struct percpu, stm)) \
+         : );                       \
+                                    \
+    val_;                           \
+MACRO_END
+
+#define percpu_ptr(typ, stm)        \
+MACRO_BEGIN                         \
+    typ *ptr_ = (typ *)__builtin_offsetof(struct percpu, stm); \
+                                    \
+    asm("add %%gs:0, %[pointer]"    \
+         : [pointer] "+r" (ptr_)    \
+         : /* No inputs */          \
+         : );                       \
+                                    \
+    ptr_;                           \
+MACRO_END
+
+#include <kern/processor.h>
+#include <kern/thread.h>
+
+struct percpu {
+    struct percpu	*self;
+    int			apic_id;
+    int			cpu_id;
+    struct processor	processor;
+/*
+    struct machine_slot	machine_slot;
+    struct mp_desc_table mp_desc_table;
+    thread_t		active_thread;
+    vm_offset_t		active_stack;
+    vm_offset_t		int_stack_top;
+    vm_offset_t		int_stack_base;
+    ast_t		need_ast;
+    ipc_kmsg_t		ipc_kmsg_cache;
+    pmap_update_list	cpu_update_list;
+    spl_t		saved_ipl;
+    spl_t		curr_ipl;
+    timer_data_t	kernel_timer;
+    timer_t		current_timer;
+    unsigned long	in_interrupt;
+*/
+};
+
+extern struct percpu percpu_array[NCPUS];
+
+void init_percpu(int cpu);
+
+#endif /* _PERCPU_H_ */
diff --git a/i386/i386/pit.c b/i386/i386/pit.c
index 6c006a98..9e527fca 100644
--- a/i386/i386/pit.c
+++ b/i386/i386/pit.c
@@ -118,7 +118,7 @@ pit_mdelay(int msec)
 void
 clkstart(void)
 {
-	if (cpu_number() != 0)
+	if (cpu_number_slow() != 0)
 		/* Only one PIT initialization is needed */
 		return;
 	unsigned char	byte;
diff --git a/i386/i386/spl.S b/i386/i386/spl.S
index 2f2c8e3a..9ce780f4 100644
--- a/i386/i386/spl.S
+++ b/i386/i386/spl.S
@@ -48,7 +48,7 @@ lock	orl	$1,hyp_shared_info+CPU_PENDING_SEL; /* Yes, activate it */ \
 
 ENTRY(spl0)
 	mb;
-	CPU_NUMBER(%edx)
+	CPU_NUMBER_NO_GS(%edx)
 	movl	CX(EXT(curr_ipl),%edx),%eax	/* save current ipl */
 	pushl	%eax
 	cli				/* disable interrupts */
@@ -77,7 +77,7 @@ ENTRY(spl0)
 #endif
 	cli				/* disable interrupts */
 1:
-	CPU_NUMBER(%edx)
+	CPU_NUMBER_NO_GS(%edx)
 	cmpl	$(SPL0),CX(EXT(curr_ipl),%edx)	/* are we at spl0? */
 	je	1f				/* yes, all done */
 	movl	$(SPL0),CX(EXT(curr_ipl),%edx)	/* set ipl */
@@ -123,14 +123,14 @@ ENTRY(spl7)
 	mb;
 	/* just clear IF */
 	cli
-	CPU_NUMBER(%edx)
+	CPU_NUMBER_NO_GS(%edx)
 	movl    $SPL7,%eax
 	xchgl   CX(EXT(curr_ipl),%edx),%eax
 	ret
 
 ENTRY(splx)
 	movl	S_ARG0,%edx		/* get ipl */
-	CPU_NUMBER(%eax)
+	CPU_NUMBER_NO_GS(%eax)
 #if (MACH_KDB || MACH_TTD) && !defined(MACH_XEN)
 	/* First make sure that if we're exitting from ipl7, IF is still cleared */
 	cmpl	$SPL7,CX(EXT(curr_ipl),%eax)	/* from ipl7? */
@@ -145,7 +145,7 @@ ENTRY(splx)
 #endif	/* (MACH_KDB || MACH_TTD) && !MACH_XEN */
 	testl	%edx,%edx		/* spl0? */
 	jz	EXT(spl0)		/* yes, handle specially */
-	CPU_NUMBER(%eax)
+	CPU_NUMBER_NO_GS(%eax)
 	cmpl	CX(EXT(curr_ipl),%eax),%edx	/* same ipl as current? */
 	jne	spl			/* no */
 	cmpl	$SPL7,%edx		/* spl7? */
@@ -194,7 +194,7 @@ splx_cli:
 1:
 	xorl	%edx,%edx		/* edx = ipl 0 */
 2:
-	CPU_NUMBER(%eax)
+	CPU_NUMBER_NO_GS(%eax)
 	cmpl	CX(EXT(curr_ipl),%eax),%edx	/* same ipl as current? */
 	je	1f				/* yes, all done */
 	movl	%edx,CX(EXT(curr_ipl),%eax)	/* set ipl */
@@ -213,7 +213,7 @@ splx_cli:
 	.align	TEXT_ALIGN
 	.globl	spl
 spl:
-	CPU_NUMBER(%eax)
+	CPU_NUMBER_NO_GS(%eax)
 #if (MACH_KDB || MACH_TTD) && !defined(MACH_XEN)
 	/* First make sure that if we're exitting from ipl7, IF is still cleared */
 	cmpl	$SPL7,CX(EXT(curr_ipl),%eax)	/* from ipl7? */
@@ -233,7 +233,7 @@ spl:
 					/* get int mask */
 #endif
 	cli				/* disable interrupts */
-	CPU_NUMBER(%eax)
+	CPU_NUMBER_NO_GS(%eax)
 	xchgl	CX(EXT(curr_ipl),%eax),%edx	/* set ipl */
 #ifdef MACH_XEN
 	XEN_SETMASK()			/* program PICs with new mask */
diff --git a/i386/i386at/model_dep.c b/i386/i386at/model_dep.c
index f83214b1..97acfdd6 100644
--- a/i386/i386at/model_dep.c
+++ b/i386/i386at/model_dep.c
@@ -462,6 +462,7 @@ i386at_init(void)
 	ldt_init();
 	ktss_init();
 
+	init_percpu(0);
 #if NCPUS > 1
 	/* Initialize SMP structures in the master processor */
 	mp_desc_init(0);