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

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Date:	Fri, 16 Apr 2010 21:34:56 +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 9:21 PM, jamal <hadi@...erus.ca> wrote:
> On Fri, 2010-04-16 at 07:18 +0200, Eric Dumazet wrote:
>
>>
>> A kernel module might do this, this could be integrated in perf bench so
>> that we can regression tests upcoming kernels.
>
> Perf would be good - but even softnet_stat cleaner than the the nasty
> hack i use (attached) would be a good start; the ping with and without
> rps gives me a ballpark number.
>
> IPI is important to me because having tried it before it and failed
> miserably. I was thinking the improvement may be due to hardware used
> but i am having a hard time to get people to tell me what hardware they
> used! I am old school - I need data;-> The RFS patch commit seems to
> have more info but still vague, example:
> "The benefits of RFS are dependent on cache hierarchy, application
> load, and other factors"
> Also, what does a "simple" or "complex" benchmark mean?;->
> I think it is only fair to get this info, no?
>
> Please dont consider what i say above as being anti-RPS.
> 5 microsec extra latency is not bad if it can be amortized.
> Unfortunately, the best traffic i could generate was < 20Kpps of
> ping which still manages to get 1 IPI/packet on Nehalem. I am going
> to write up some app (lots of cycles available tommorow). I still think
> it is valueable.
>

+	seq_printf(seq, "%08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x\n",
 		   s->total, s->dropped, s->time_squeeze, 0,
 		   0, 0, 0, 0, /* was fastroute */
-		   s->cpu_collision, s->received_rps);
+		   s->cpu_collision, s->received_rps, s->ipi_rps);

Do you mean that received_rps is equal to ipi_rps? received_rps is the
number of IPI used by RPS. And ipi_rps is the number of IPIs sent by
function generic_exec_single(). If there isn't other user of
generic_exec_single(), received_rps should be equal to ipi_rps.

@@ -158,7 +159,10 @@ void generic_exec_single(int cpu, struct
call_single_data *data, int wait)
 	 * equipped to do the right thing...
 	 */
 	if (ipi)
+{
 		arch_send_call_function_single_ipi(cpu);
+		__get_cpu_var(netdev_rx_stat).ipi_rps++;
+}


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