linux-kernel - Re: Re: [PATCH v2] bit_spinlock: introduce smp_cond_load

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Message-ID: <f30835ca-f6e8-1e31-3364-cb1d958d76bf@aol.com>
Date:   Tue, 6 Nov 2018 01:11:44 +0800
From:   Gao Xiang <hsiangkao@....com>
To:     Gao Xiang <gaoxiang25@...wei.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Philippe Ombredanne <pombredanne@...b.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Miao Xie <miaoxie@...wei.com>, Chao Yu <chao@...nel.org>
Subject: Re: Re: [PATCH v2] bit_spinlock: introduce smp_cond_load_relaxed

Hi all,

ping... is there someone interested in this patch?

It seems bit_spinlock performs much better by using
smp_cond_load_relaxed than just do busy-loop in arm64...

Thanks,
Gao Xiang

On 2018/10/30 13:52, Gao Xiang wrote:
> Hi,
> 
> On 2018/10/30 14:04, Gao Xiang wrote:
>> It is better to use wrapped smp_cond_load_relaxed
>> instead of open-coded busy waiting for bit_spinlock.
>>
>> Signed-off-by: Gao Xiang <gaoxiang25@...wei.com>
>> ---
>>
>> change log v2:
>>  - fix the incorrect expression !(VAL >> (bitnum & (BITS_PER_LONG-1)))
>>  - the test result is described in the following reply.
>>
>> Thanks,
>> Gao Xiang
> 
> 
> Simple test script:
> #include <linux/kthread.h>
> #include <linux/bit_spinlock.h>
> #include <linux/module.h>
> 
> unsigned long global_lock;
> 
> int test_thread(void *data)
> {
> 	unsigned long thread_id = (unsigned long)data;
> 	int i;
> 	u64 start = ktime_get_ns();
> 
> 	for (i = 0; i < 500000; ++i) {
> 		bit_spin_lock(0, &global_lock);
> 		__asm__("yield");
> 		bit_spin_unlock(0, &global_lock);
> 	}
> 	pr_err("Thread id: %lu time: %llu\n", thread_id, ktime_get_ns() - start);
> 
> 	do_exit(0);
> }
> 
> 
> static int __init bitspinlock_test_module_init(void)
> {
> 	int i;
> 
> 	for (i = 0; i < 8; ++i) {
> 		if (IS_ERR(kthread_run(test_thread, (void *)(unsigned long)i, "thread-%d", i)))
> 			pr_err("fail to create thread %d\n", i);
> 	}
> 
> 	return 0;
> }
> 
> static void __exit bitspinlock_test_module_exit(void)
> {
> }
> 
> module_init(bitspinlock_test_module_init);
> module_exit(bitspinlock_test_module_exit);
> MODULE_LICENSE("GPL");
> 
> 
> ...and tested in the following ARM server environment:
> 
> Processor: HI1616 (https://en.wikichip.org/wiki/hisilicon/hi16xx/hi1616)
> Board: HiSilicon D05 Development Board (http://open-estuary.org/d05/)
> Memory: 512GB
> Host OS: Ubuntu 18.04.1 LTS (Ubuntu 4.15.0-29.31-generic 4.15.18)
> QEMU KVM OS: Linux 4.19 + buildroot
> QEMU KVM cmdline: qemu-system-aarch64 -enable-kvm -cpu host -smp 4 -m 256M -kernel Image -M virt,kernel_irqchip=on -nographic -hda rootfs.ext2 -append 'root=/dev/vda console=ttyAMA0 earlycon=pl011,0x9000000' -serial mon:stdio -net none
> 
> Without this patch:
>   Thread 0   Thread 1   Thread 2   Thread 3   Thread 4   Thread 5   Thread 6   Thread 7
> 1 1283709480 1271869280  454742480 1173673820 1145643640 1118846920  774616920 1144146140
> 2  643580180  625143860  576841700  322982340  649987880  585749000  529178880  373374780
> 3  672307220  847315000  880801860 1039502040  667086380 1033939940 1035381120 1046898300
> 4  568635580  440547020  737000380  910040880  804543740  712314280  868896880  867049000
> 5  749107320  726397720  776134480  611970100  756721040  753449440  711691300  609343300
> 
> With this patch:
>   Thread 0   Thread 1   Thread 2   Thread 3   Thread 4   Thread 5   Thread 6   Thread 7
> 1  170327620  196322160  169434180   74723860  178145600  178873460  143843260   70998780
> 2  166415220  129649200  166161240  175241520  155474460  112811860  157003140  150087420
> 3  511420780  117655640  598641860  596213720  462888760  430838600  554346300  428035120 
> 4  174520240  156311800  120274280   87465380  172781400  136118620  163728340   63026360
> 5  153677940  202786860  183626500  140721300  150311360  161266840  168154340  107247460
> 
> Thanks,
> Gao Xiang
>