netdev - Re: [PATCH v6] net: batch skb dequeueing from softnet input_pkt

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Date:	Sun, 02 May 2010 12:54:50 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	David Miller <davem@...emloft.net>, hadi@...erus.ca,
	xiaosuo@...il.com, therbert@...gle.com, shemminger@...tta.com,
	netdev@...r.kernel.org, lenb@...nel.org, arjan@...radead.org
Subject: Re: [PATCH v6] net: batch skb dequeueing from softnet
 input_pkt_queue

Le dimanche 02 mai 2010 à 11:20 +0200, Andi Kleen a écrit :
> > I tried it on the right spot (since my bench was only doing recvmsg()
> > calls, I had to patch wait_for_packet() in net/core/datagram.c
> > 
> > udp_recvmsg -> __skb_recv_datagram -> wait_for_packet ->
> > schedule_timeout
> > 
> > Unfortunatly, using io_schedule_timeout() did not solve the problem.
> 
> Hmm, too bad. Weird.
> 
> > 
> > Tell me if you need some traces or something.
> 
> I'll try to reproduce it and see what I can do.
> 

Here the perf report on the latest test done, I confirm I am using
io_schedule_timeout() in this kernel.

In this test, all 16 queues of one BCM57711E NIC (1Gb link) delivers
 packets at about 1.300.000 pps to 16 cpus (one cpu per queue) and these
packets are then redistributed by RPS to same 16 cpus, generating about
650.000 IPI per second.

top says :
Cpu(s):  3.0%us, 17.3%sy,  0.0%ni, 22.4%id, 28.2%wa,  0.0%hi, 29.1%si,
0.0%st


# Samples: 321362570767
#
# Overhead         Command                 Shared Object  Symbol
# ........  ..............  ............................  ......
#
    25.08%            init  [kernel.kallsyms]             [k] _raw_spin_lock_irqsave
                      |
                      --- _raw_spin_lock_irqsave
                         |          
                         |--93.47%-- clockevents_notify
                         |          lapic_timer_state_broadcast
                         |          acpi_idle_enter_bm
                         |          cpuidle_idle_call
                         |          cpu_idle
                         |          start_secondary
                         |          
                         |--4.70%-- tick_broadcast_oneshot_control
                         |          tick_notify
                         |          notifier_call_chain
                         |          __raw_notifier_call_chain
                         |          raw_notifier_call_chain
                         |          clockevents_do_notify
                         |          clockevents_notify
                         |          lapic_timer_state_broadcast
                         |          acpi_idle_enter_bm
                         |          cpuidle_idle_call
                         |          cpu_idle
                         |          start_secondary
                         |          
                         |--0.64%-- generic_exec_single
                         |          __smp_call_function_single
                         |          net_rps_action_and_irq_enable
...
     9.72%            init  [kernel.kallsyms]             [k] acpi_os_read_port
                      |
                      --- acpi_os_read_port
                         |          
                         |--99.45%-- acpi_hw_read_port
                         |          acpi_hw_read
                         |          acpi_hw_read_multiple
                         |          acpi_hw_register_read
                         |          acpi_read_bit_register
                         |          acpi_idle_enter_bm
                         |          cpuidle_idle_call
                         |          cpu_idle
                         |          start_secondary
                         |          
                          --0.55%-- acpi_hw_read
                                    acpi_hw_read_multiple

powertop says :
     PowerTOP version 1.11      (C) 2007 Intel Corporation

Cn                Avg residency       P-states (frequencies)
C0 (cpu running)        (68.9%)         2.93 Ghz    46.5%
polling           0.0ms ( 0.0%)         2.80 Ghz     5.1%
C1 mwait          0.0ms ( 0.0%)         2.53 Ghz     3.0%
C2 mwait          0.0ms (31.1%)         2.13 Ghz     2.8%
                                        1.60 Ghz    38.2%

Wakeups-from-idle per second : 45177.8  interval: 5.0s
no ACPI power usage estimate available

Top causes for wakeups:
   9.9% (40863.0)       <interrupt> : eth1-fp-7 
   9.9% (40861.0)       <interrupt> : eth1-fp-8 
   9.9% (40858.0)       <interrupt> : eth1-fp-5 
   9.9% (40855.2)       <interrupt> : eth1-fp-10 
   9.9% (40847.6)       <interrupt> : eth1-fp-14 
   9.9% (40847.2)       <interrupt> : eth1-fp-12 
   9.9% (40835.0)       <interrupt> : eth1-fp-1 
   9.9% (40834.2)       <interrupt> : eth1-fp-3 
   9.9% (40834.0)       <interrupt> : eth1-fp-6 
   9.9% (40829.6)       <interrupt> : eth1-fp-4 
   1.0% (4002.0)     <kernel core> : hrtimer_start_range_ns (tick_sched_timer) 
   0.4% (1725.6)       <interrupt> : extra timer interrupt 
   0.0% (  4.0)     <kernel core> : usb_hcd_poll_rh_status (rh_timer_func)
   0.0% (  2.0)     <kernel core> : clocksource_watchdog (clocksource_watchdog)
   0.0% (  2.0)             snmpd : hrtimer_start_range_ns (hrtimer_wakeup)


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