linux-kernel - Re: [PATCH] x86: Run checksumming in parallel accross multiple alu's

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Date:	Fri, 18 Oct 2013 14:15:52 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Neil Horman <nhorman@...driver.com>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	sebastien.dugue@...l.net, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [PATCH] x86: Run checksumming in parallel accross multiple alu's

On Fri, 2013-10-18 at 16:11 -0400, Neil Horman wrote:

> #define BUFSIZ_ORDER 4
> #define BUFSIZ ((2 << BUFSIZ_ORDER) * (1024*1024*2))
> static int __init csum_init_module(void)
> {
> 	int i;
> 	__wsum sum = 0;
> 	struct timespec start, end;
> 	u64 time;
> 	struct page *page;
> 	u32 offset = 0;
> 
> 	page = alloc_pages((GFP_TRANSHUGE & ~__GFP_MOVABLE), BUFSIZ_ORDER);

Not sure what you are doing here, but its not correct.

You have a lot of variations in your results, I suspect a NUMA affinity
problem.

You can try the following code, and use taskset to make sure you run
this on a cpu on node 0

#define BUFSIZ 2*1024*1024
#define NBPAGES 16

static int __init csum_init_module(void)
{
        int i;
        __wsum sum = 0;
        u64 start, end;
	void *base, *addrs[NBPAGES];
        u32 rnd, offset;

	memset(addrs, 0, sizeof(addrs));
	for (i = 0; i < NBPAGES; i++) {
		addrs[i] = kmalloc_node(BUFSIZ, GFP_KERNEL, 0);
		if (!addrs[i])
			goto out;
	}

        local_bh_disable();
        pr_err("STARTING ITERATIONS on cpu %d\n", smp_processor_id());
        start = ktime_to_ns(ktime_get());
        
        for (i = 0; i < 100000; i++) {
		rnd = prandom_u32();
		base = addrs[rnd % NBPAGES];
		rnd /= NBPAGES;
		offset = rnd % (BUFSIZ - 1500);
                offset &= ~1U;
                sum = csum_partial_opt(base + offset, 1500, sum);
        }
        end = ktime_to_ns(ktime_get());
        local_bh_enable();

        pr_err("COMPLETED 100000 iterations of csum %x in %llu nanosec\n", sum, end - start);

out:
	for (i = 0; i < NBPAGES; i++)
		kfree(addrs[i]);

        return 0;
}

static void __exit csum_cleanup_module(void)
{
        return;
}



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