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SubjectRe: [BENCHMARK] Lmbench 2.5.54-mm2 (impressive improvements)
Andi Kleen wrote:
>
> P.S.: regarding recent lmbench slow downs: I'm a bit
> worried about the two wrmsrs which are in the i386 context switch
> in load_esp0 for sysenter now. Last time I benchmarked WRMSRs on
> Athlon they were really slow and knowing the P4 it is probably
> even slower there. Imho it would be better to undo that patch
> and use Linus' original trampoline stack.
>

Looks like you're right. The indications are that this change
has slowed context switches by ~5% on a PIII. The backout patch
against 2.5.54 is below. Testing on a P4 would be useful.

2.5.54, stock:

lmbench:

Context switching - times in microseconds - smaller is better
-------------------------------------------------------------
Host OS 2p/0K 2p/16K 2p/64K 8p/16K 8p/64K 16p/16K 16p/64K
ctxsw ctxsw ctxsw ctxsw ctxsw ctxsw ctxsw
--------- ------------- ----- ------ ------ ------ ------ ------- -------
i686-linu Linux 2.5.54 3 16 44 18 47 20 77

*Local* Communication latencies in microseconds - smaller is better
-------------------------------------------------------------------
Host OS 2p/0K Pipe AF UDP RPC/ TCP RPC/ TCP
ctxsw UNIX UDP TCP conn
--------- ------------- ----- ----- ---- ----- ----- ----- ----- ----
i686-linu Linux 2.5.54 3 16 26 65 78 231

AIM9:

3 tcp_test 10.00 2767 276.70000 24903.00 TCP/IP Messages/second
4 udp_test 10.00 4658 465.80000 46580.00 UDP/IP DataGrams/second
5 fifo_test 10.01 6507 650.04995 65005.00 FIFO Messages/second
6 dgram_pipe 10.00 11228 1122.80000 112280.00 DataGram Pipe Messages/second
7 pipe_cpy 10.00 15463 1546.30000 154630.00 Pipe Messages/second

pollbench:
pollbench 1 100 5000
result with handles 1 processes 100 loops 5000:time 9.609487 sec.
pollbench 2 100 2000
result with handles 2 processes 100 loops 2000:time 4.016496 sec.
pollbench 5 100 2000
result with handles 5 processes 100 loops 2000:time 4.917921 sec.


2.5.54, with the below backout patch:

Context switching - times in microseconds - smaller is better
-------------------------------------------------------------
Host OS 2p/0K 2p/16K 2p/64K 8p/16K 8p/64K 16p/16K 16p/64K
ctxsw ctxsw ctxsw ctxsw ctxsw ctxsw ctxsw
--------- ------------- ----- ------ ------ ------ ------ ------- -------
i686-linu Linux 2.5.54 3 14 47 18 50 20 61

*Local* Communication latencies in microseconds - smaller is better
-------------------------------------------------------------------
Host OS 2p/0K Pipe AF UDP RPC/ TCP RPC/ TCP
ctxsw UNIX UDP TCP conn
--------- ------------- ----- ----- ---- ----- ----- ----- ----- ----
i686-linu Linux 2.5.54 3 15 25 64 69 231


3 tcp_test 10.00 2908 290.80000 26172.00 TCP/IP Messages/second
4 udp_test 10.00 4971 497.10000 49710.00 UDP/IP DataGrams/second
5 fifo_test 10.01 6642 663.53646 66353.65 FIFO Messages/second
6 dgram_pipe 10.00 11516 1151.60000 115160.00 DataGram Pipe Messages/second
7 pipe_cpy 10.00 15930 1593.00000 159300.00 Pipe Messages/second


pollbench 1 100 5000
result with handles 1 processes 100 loops 5000:time 9.106732 sec.
pollbench 2 100 2000
result with handles 2 processes 100 loops 2000:time 3.853814 sec.
pollbench 5 100 2000
result with handles 5 processes 100 loops 2000:time 4.533519 sec.



arch/i386/kernel/cpu/common.c | 2 +-
arch/i386/kernel/process.c | 2 +-
arch/i386/kernel/sysenter.c | 34 ++++++++++++++++++++++++++++++----
arch/i386/kernel/vm86.c | 4 +---
include/asm-i386/cpufeature.h | 3 ---
include/asm-i386/msr.h | 4 ----
include/asm-i386/processor.h | 16 ----------------
7 files changed, 33 insertions(+), 32 deletions(-)

--- 25/arch/i386/kernel/cpu/common.c~bad3 Fri Jan 3 16:36:48 2003
+++ 25-akpm/arch/i386/kernel/cpu/common.c Fri Jan 3 16:36:48 2003
@@ -484,7 +484,7 @@ void __init cpu_init (void)
BUG();
enter_lazy_tlb(&init_mm, current, cpu);

- load_esp0(t, thread->esp0);
+ t->esp0 = thread->esp0;
set_tss_desc(cpu,t);
cpu_gdt_table[cpu][GDT_ENTRY_TSS].b &= 0xfffffdff;
load_TR_desc();
--- 25/arch/i386/kernel/process.c~bad3 Fri Jan 3 16:36:48 2003
+++ 25-akpm/arch/i386/kernel/process.c Fri Jan 3 16:36:48 2003
@@ -437,7 +437,7 @@ void __switch_to(struct task_struct *pre
/*
* Reload esp0, LDT and the page table pointer:
*/
- load_esp0(tss, next->esp0);
+ tss->esp0 = next->esp0;

/*
* Load the per-thread Thread-Local Storage descriptor.
--- 25/arch/i386/kernel/sysenter.c~bad3 Fri Jan 3 16:36:48 2003
+++ 25-akpm/arch/i386/kernel/sysenter.c Fri Jan 3 16:36:48 2003
@@ -34,14 +34,40 @@ struct fake_sep_struct {
unsigned char stack[0];
} __attribute__((aligned(8192)));

+static struct fake_sep_struct *alloc_sep_thread(int cpu)
+{
+ struct fake_sep_struct *entry;
+
+ entry = (struct fake_sep_struct *) __get_free_pages(GFP_ATOMIC, 1);
+ if (!entry)
+ return NULL;
+
+ memset(entry, 0, PAGE_SIZE<<1);
+ entry->thread.task = &entry->task;
+ entry->task.thread_info = &entry->thread;
+ entry->thread.preempt_count = 1;
+ entry->thread.cpu = cpu;
+
+ return entry;
+}
+
static void __init enable_sep_cpu(void *info)
{
int cpu = get_cpu();
- struct tss_struct *tss = init_tss + cpu;
+ struct fake_sep_struct *sep = alloc_sep_thread(cpu);
+ unsigned long *esp0_ptr = &(init_tss + cpu)->esp0;
+ unsigned long rel32;
+
+ rel32 = (unsigned long) sysenter_entry - (unsigned long) (sep->trampoline+11);
+
+ *(short *) (sep->trampoline+0) = 0x258b; /* movl xxxxx,%esp */
+ *(long **) (sep->trampoline+2) = esp0_ptr;
+ *(char *) (sep->trampoline+6) = 0xe9; /* jmp rl32 */
+ *(long *) (sep->trampoline+7) = rel32;

- wrmsr(MSR_IA32_SYSENTER_CS, __KERNEL_CS, 0);
- wrmsr(MSR_IA32_SYSENTER_ESP, tss->esp0, 0);
- wrmsr(MSR_IA32_SYSENTER_EIP, (unsigned long) sysenter_entry, 0);
+ wrmsr(0x174, __KERNEL_CS, 0); /* SYSENTER_CS_MSR */
+ wrmsr(0x175, PAGE_SIZE*2 + (unsigned long) sep, 0); /* SYSENTER_ESP_MSR */
+ wrmsr(0x176, (unsigned long) &sep->trampoline, 0); /* SYSENTER_EIP_MSR */

printk("Enabling SEP on CPU %d\n", cpu);
put_cpu();
--- 25/arch/i386/kernel/vm86.c~bad3 Fri Jan 3 16:36:48 2003
+++ 25-akpm/arch/i386/kernel/vm86.c Fri Jan 3 16:36:48 2003
@@ -113,8 +113,7 @@ struct pt_regs * save_v86_state(struct k
do_exit(SIGSEGV);
}
tss = init_tss + smp_processor_id();
- current->thread.esp0 = current->thread.saved_esp0;
- load_esp0(tss, current->thread.esp0);
+ tss->esp0 = current->thread.esp0 = current->thread.saved_esp0;
current->thread.saved_esp0 = 0;
loadsegment(fs, current->thread.saved_fs);
loadsegment(gs, current->thread.saved_gs);
@@ -290,7 +289,6 @@ static void do_sys_vm86(struct kernel_vm

tss = init_tss + smp_processor_id();
tss->esp0 = tsk->thread.esp0 = (unsigned long) &info->VM86_TSS_ESP0;
- disable_sysenter();

tsk->thread.screen_bitmap = info->screen_bitmap;
if (info->flags & VM86_SCREEN_BITMAP)
--- 25/include/asm-i386/cpufeature.h~bad3 Fri Jan 3 16:36:48 2003
+++ 25-akpm/include/asm-i386/cpufeature.h Fri Jan 3 16:36:48 2003
@@ -7,8 +7,6 @@
#ifndef __ASM_I386_CPUFEATURE_H
#define __ASM_I386_CPUFEATURE_H

-#include <linux/bitops.h>
-
#define NCAPINTS 4 /* Currently we have 4 32-bit words worth of info */

/* Intel-defined CPU features, CPUID level 0x00000001, word 0 */
@@ -77,7 +75,6 @@
#define cpu_has_pge boot_cpu_has(X86_FEATURE_PGE)
#define cpu_has_sse2 boot_cpu_has(X86_FEATURE_XMM2)
#define cpu_has_apic boot_cpu_has(X86_FEATURE_APIC)
-#define cpu_has_sep boot_cpu_has(X86_FEATURE_SEP)
#define cpu_has_mtrr boot_cpu_has(X86_FEATURE_MTRR)
#define cpu_has_mmx boot_cpu_has(X86_FEATURE_MMX)
#define cpu_has_fxsr boot_cpu_has(X86_FEATURE_FXSR)
--- 25/include/asm-i386/msr.h~bad3 Fri Jan 3 16:36:48 2003
+++ 25-akpm/include/asm-i386/msr.h Fri Jan 3 16:36:48 2003
@@ -53,10 +53,6 @@

#define MSR_IA32_BBL_CR_CTL 0x119

-#define MSR_IA32_SYSENTER_CS 0x174
-#define MSR_IA32_SYSENTER_ESP 0x175
-#define MSR_IA32_SYSENTER_EIP 0x176
-
#define MSR_IA32_MCG_CAP 0x179
#define MSR_IA32_MCG_STATUS 0x17a
#define MSR_IA32_MCG_CTL 0x17b
--- 25/include/asm-i386/processor.h~bad3 Fri Jan 3 16:36:48 2003
+++ 25-akpm/include/asm-i386/processor.h Fri Jan 3 16:36:48 2003
@@ -14,7 +14,6 @@
#include <asm/types.h>
#include <asm/sigcontext.h>
#include <asm/cpufeature.h>
-#include <asm/msr.h>
#include <linux/cache.h>
#include <linux/config.h>
#include <linux/threads.h>
@@ -411,21 +410,6 @@ struct thread_struct {
.io_bitmap = { [ 0 ... IO_BITMAP_SIZE ] = ~0 }, \
}

-static inline void load_esp0(struct tss_struct *tss, unsigned long esp0)
-{
- tss->esp0 = esp0;
- if (cpu_has_sep) {
- wrmsr(MSR_IA32_SYSENTER_CS, __KERNEL_CS, 0);
- wrmsr(MSR_IA32_SYSENTER_ESP, esp0, 0);
- }
-}
-
-static inline void disable_sysenter(void)
-{
- if (cpu_has_sep)
- wrmsr(MSR_IA32_SYSENTER_CS, 0, 0);
-}
-
#define start_thread(regs, new_eip, new_esp) do { \
__asm__("movl %0,%%fs ; movl %0,%%gs": :"r" (0)); \
set_fs(USER_DS); \
_
-
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