Messages in this thread | | | Date | Mon, 16 Mar 2009 21:32:20 -0400 | From | Mathieu Desnoyers <> | Subject | cli/sti vs local_cmpxchg and local_add_return |
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Hi,
I am trying to get access to some non-x86 hardware to run some atomic primitive benchmarks for a paper on LTTng I am preparing. That should be useful to argue about performance benefit of per-cpu atomic operations vs interrupt disabling. I would like to run the following benchmark module on CONFIG_SMP :
- PowerPC - MIPS - ia64 - alpha
usage : make insmod test-cmpxchg-nolock.ko insmod: error inserting 'test-cmpxchg-nolock.ko': -1 Resource temporarily unavailable dmesg (see dmesg output)
If some of you would be kind enough to run my test module provided below and provide the results of these tests on a recent kernel (2.6.26~2.6.29 should be good) along with their cpuinfo, I would greatly appreciate.
Here are the CAS results for various Intel-based architectures :
Architecture | Speedup | CAS | Interrupts | | (cli + sti) / local cmpxchg | local | sync | Enable (sti) | Disable (cli) ------------------------------------------------------------------------------------------------- Intel Pentium 4 | 5.24 | 25 | 81 | 70 | 61 | AMD Athlon(tm)64 X2 | 4.57 | 7 | 17 | 17 | 15 | Intel Core2 | 6.33 | 6 | 30 | 20 | 18 | Intel Xeon E5405 | 5.25 | 8 | 24 | 20 | 22 |
The benefit expected on PowerPC, ia64 and alpha should principally come from removed memory barriers in the local primitives.
Thanks,
Mathieu
P.S. please forgive the coding style and hackish interface. :)
/* test-cmpxchg-nolock.c * * Compare local cmpxchg with irq disable / enable. */
#include <linux/jiffies.h> #include <linux/compiler.h> #include <linux/init.h> #include <linux/module.h> #include <linux/math64.h> #include <asm/timex.h> #include <asm/system.h>
#define NR_LOOPS 20000
int test_val;
static void do_testbaseline(void) { unsigned long flags; unsigned int i; cycles_t time1, time2, time; u32 rem;
local_irq_save(flags); preempt_disable(); time1 = get_cycles(); for (i = 0; i < NR_LOOPS; i++) { asm volatile (""); } time2 = get_cycles(); local_irq_restore(flags); preempt_enable(); time = time2 - time1;
printk(KERN_ALERT "test results: time for baseline\n"); printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS); printk(KERN_ALERT "total time: %llu\n", time); time = div_u64_rem(time, NR_LOOPS, &rem); printk(KERN_ALERT "-> baseline takes %llu cycles\n", time); printk(KERN_ALERT "test end\n"); }
static void do_test_sync_cmpxchg(void) { int ret; unsigned long flags; unsigned int i; cycles_t time1, time2, time; u32 rem;
local_irq_save(flags); preempt_disable(); time1 = get_cycles(); for (i = 0; i < NR_LOOPS; i++) { #ifdef CONFIG_X86_32 ret = sync_cmpxchg(&test_val, 0, 0); #else ret = cmpxchg(&test_val, 0, 0); #endif } time2 = get_cycles(); local_irq_restore(flags); preempt_enable(); time = time2 - time1;
printk(KERN_ALERT "test results: time for locked cmpxchg\n"); printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS); printk(KERN_ALERT "total time: %llu\n", time); time = div_u64_rem(time, NR_LOOPS, &rem); printk(KERN_ALERT "-> locked cmpxchg takes %llu cycles\n", time); printk(KERN_ALERT "test end\n"); }
static void do_test_cmpxchg(void) { int ret; unsigned long flags; unsigned int i; cycles_t time1, time2, time; u32 rem;
local_irq_save(flags); preempt_disable(); time1 = get_cycles(); for (i = 0; i < NR_LOOPS; i++) { ret = cmpxchg_local(&test_val, 0, 0); } time2 = get_cycles(); local_irq_restore(flags); preempt_enable(); time = time2 - time1;
printk(KERN_ALERT "test results: time for non locked cmpxchg\n"); printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS); printk(KERN_ALERT "total time: %llu\n", time); time = div_u64_rem(time, NR_LOOPS, &rem); printk(KERN_ALERT "-> non locked cmpxchg takes %llu cycles\n", time); printk(KERN_ALERT "test end\n"); } static void do_test_sync_inc(void) { int ret; unsigned long flags; unsigned int i; cycles_t time1, time2, time; u32 rem; atomic_t val;
local_irq_save(flags); preempt_disable(); time1 = get_cycles(); for (i = 0; i < NR_LOOPS; i++) { ret = atomic_add_return(10, &val); } time2 = get_cycles(); local_irq_restore(flags); preempt_enable(); time = time2 - time1;
printk(KERN_ALERT "test results: time for locked add return\n"); printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS); printk(KERN_ALERT "total time: %llu\n", time); time = div_u64_rem(time, NR_LOOPS, &rem); printk(KERN_ALERT "-> locked add return takes %llu cycles\n", time); printk(KERN_ALERT "test end\n"); }
static void do_test_inc(void) { int ret; unsigned long flags; unsigned int i; cycles_t time1, time2, time; u32 rem; local_t loc_val;
local_irq_save(flags); preempt_disable(); time1 = get_cycles(); for (i = 0; i < NR_LOOPS; i++) { ret = local_add_return(10, &loc_val); } time2 = get_cycles(); local_irq_restore(flags); preempt_enable(); time = time2 - time1;
printk(KERN_ALERT "test results: time for non locked add return\n"); printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS); printk(KERN_ALERT "total time: %llu\n", time); time = div_u64_rem(time, NR_LOOPS, &rem); printk(KERN_ALERT "-> non locked add return takes %llu cycles\n", time); printk(KERN_ALERT "test end\n"); }
/* * This test will have a higher standard deviation due to incoming interrupts. */ static void do_test_enable_int(void) { unsigned long flags; unsigned int i; cycles_t time1, time2, time; u32 rem;
local_irq_save(flags); preempt_disable(); time1 = get_cycles(); for (i = 0; i < NR_LOOPS; i++) { local_irq_restore(flags); } time2 = get_cycles(); local_irq_restore(flags); preempt_enable(); time = time2 - time1;
printk(KERN_ALERT "test results: time for enabling interrupts (STI)\n"); printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS); printk(KERN_ALERT "total time: %llu\n", time); time = div_u64_rem(time, NR_LOOPS, &rem); printk(KERN_ALERT "-> enabling interrupts (STI) takes %llu cycles\n", time); printk(KERN_ALERT "test end\n"); }
static void do_test_disable_int(void) { unsigned long flags, flags2; unsigned int i; cycles_t time1, time2, time; u32 rem;
local_irq_save(flags); preempt_disable(); time1 = get_cycles(); for ( i = 0; i < NR_LOOPS; i++) { local_irq_save(flags2); } time2 = get_cycles(); local_irq_restore(flags); preempt_enable(); time = time2 - time1;
printk(KERN_ALERT "test results: time for disabling interrupts (CLI)\n"); printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS); printk(KERN_ALERT "total time: %llu\n", time); time = div_u64_rem(time, NR_LOOPS, &rem); printk(KERN_ALERT "-> disabling interrupts (CLI) takes %llu cycles\n", time); printk(KERN_ALERT "test end\n"); }
static void do_test_int(void) { unsigned long flags; unsigned int i; cycles_t time1, time2, time; u32 rem;
local_irq_save(flags); preempt_disable(); time1 = get_cycles(); for (i = 0; i < NR_LOOPS; i++) { local_irq_restore(flags); local_irq_save(flags); } time2 = get_cycles(); local_irq_restore(flags); preempt_enable(); time = time2 - time1;
printk(KERN_ALERT "test results: time for disabling/enabling interrupts (STI/CLI)\n"); printk(KERN_ALERT "number of loops: %d\n", NR_LOOPS); printk(KERN_ALERT "total time: %llu\n", time); time = div_u64_rem(time, NR_LOOPS, &rem); printk(KERN_ALERT "-> enabling/disabling interrupts (STI/CLI) takes %llu cycles\n", time); printk(KERN_ALERT "test end\n"); }
static int ltt_test_init(void) { printk(KERN_ALERT "test init\n"); do_testbaseline(); do_test_sync_cmpxchg(); do_test_cmpxchg(); do_test_sync_inc(); do_test_inc(); do_test_enable_int(); do_test_disable_int(); do_test_int(); return -EAGAIN; /* Fail will directly unload the module */ }
static void ltt_test_exit(void) { printk(KERN_ALERT "test exit\n"); }
module_init(ltt_test_init) module_exit(ltt_test_exit)
MODULE_LICENSE("GPL"); MODULE_AUTHOR("Mathieu Desnoyers"); MODULE_DESCRIPTION("Cmpxchg vs int Test");
* Makefile
ifneq ($(KERNELRELEASE),) obj-m += test-cmpxchg-nolock.o else KERNELDIR ?= /lib/modules/$(shell uname -r)/build PWD := $(shell pwd) KERNELRELEASE = $(shell cat $(KERNELDIR)/$(KBUILD_OUTPUT)/include/linux/version.h | sed -n 's/.*UTS_RELEASE.*\"\(.*\)\".*/\1/p') ifneq ($(INSTALL_MOD_PATH),) DEPMOD_OPT := -b $(INSTALL_MOD_PATH) endif
default: $(MAKE) -C $(KERNELDIR) M=$(PWD) modules
modules_install: $(MAKE) -C $(KERNELDIR) M=$(PWD) modules_install if [ -f $(KERNELDIR)/$(KBUILD_OUTPUT)/System.map ] ; then /sbin/depmod -ae -F $(KERNELDIR)/$(KBUILD_OUTPUT)/System.map $(DEPMOD_OPT) $(KERNELRELEASE) ; fi
clean: $(MAKE) -C $(KERNELDIR) M=$(PWD) clean endif
-- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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