netdev - Re: rps perfomance WAS(Re: rps: question

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Date:	Fri, 16 Apr 2010 22:10:28 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	hadi@...erus.ca
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Rick Jones <rick.jones2@...com>,
	David Miller <davem@...emloft.net>, therbert@...gle.com,
	netdev@...r.kernel.org, robert@...julf.net, andi@...stfloor.org
Subject: Re: rps perfomance WAS(Re: rps: question

On Fri, Apr 16, 2010 at 9:49 PM, jamal <hadi@...erus.ca> wrote:
> On Fri, 2010-04-16 at 21:34 +0800, Changli Gao wrote:
>
>
> my observation is:
> s->total is the sum of all packets received by cpu (some directly from
> ethernet)

It is meaningless currently. If rps is enabled, it may be twice of the
number of the packets received, because one packet may be count twice:
one in enqueue_to_backlog(), and the other in __netif_receive_skb(). I
had posted a patch to solve this problem.

http://patchwork.ozlabs.org/patch/50217/

If you don't apply my patch, you'd better refer to /proc/net/dev for
the total number.

> s->received_rps was what the count receiver cpu saw incoming if they
> were sent by another cpu.

Maybe its name confused you.

/* Called from hardirq (IPI) context */
static void trigger_softirq(void *data)
{
        struct softnet_data *queue = data;
        __napi_schedule(&queue->backlog);
        __get_cpu_var(netdev_rx_stat).received_rps++;
}

the function above is called in IRQ of IPI. It counts the number of
IPIs received. It is actually ipi_rps you need.

> s-> ipi_rps is the times we tried to enq to remote cpu but found it to
> be empty and had to send an IPI.
> ipi_rps can be < received_rps if we receive > 1 packet without
> generating an IPI. What did i miss?
>


-- 
Regards，
Changli Gao(xiaosuo@...il.com)
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