netdev - Re: 0% cpu usasge after fresh boot or net restart but 10% CPU if kernel flush route cache

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Date:	Thu, 28 Jan 2010 11:14:27 +0200
From:	cold cold <nedkonedev@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: 0% cpu usasge after fresh boot or net restart but 10% CPU if 
	kernel flush route cache

On Wed, Jan 27, 2010 at 11:18 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le mercredi 27 janvier 2010 à 21:53 +0200, cold cold a écrit :
>
>>
>> btw atm i have 1k ip on that router but plan to put 10k so route cache
>> will grow 10 time fast.
>> i try to keep low  rhash_entries but garbage collector  is non stop
>> running and eat CPU
>> atm i have around 7k  entries per second for second for first minute.
>>
>> i think it will be better if i flush cache on secret interval instead
>> of giving work to gc.
>> i test with 512MB cache and CPU is 0% and flushing entire hash dont take a lot,
>> I'm not sure is there some side effects from flushing.
>
> Flush is immediate, it only marks entries as invalid and they are
> cleaned up later.
>
> 512 MB cache is quite small for your needs, each entry uses 384 bytes
> (assuming you use a 64bit kernel)
>
> In my experiments, I found using gc (and no flushing) was the most
> reliable way to have an equilibrium.
>
> WHen setting gc_interval to 1,  the garbage collector is fired every
> second and handles 1/300 of entries, from a work queue (thus doesnt stop
> packets to be handled by irqs), in a smooth way.
>
> You can post "perf top" results to check where cpu is consumed.
>
>
>

RX Kpps : 57 TX Kpps : 53  RX Kbits : 331184 TX Kbits : 306213
RX Kpps : 59 TX Kpps : 54  RX Kbits : 345517 TX Kbits : 304323
RX Kpps : 56 TX Kpps : 52  RX Kbits : 331418 TX Kbits : 296032
RX Kpps : 60 TX Kpps : 54  RX Kbits : 362007 TX Kbits : 297371
RX Kpps : 59 TX Kpps : 52  RX Kbits : 360455 TX Kbits : 280603


ON  one cpu, gc_interval to 1, gc_elasticity 2

Cpu0  :  0.0%us,  0.0%sy,  0.0%ni, 72.0%id,  0.0%wa,  8.3%hi, 19.7%si,  0.0%st
Cpu1  :  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu2  :  0.0%us,  0.3%sy,  0.0%ni, 99.7%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu3  :  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st

------------------------------------------------------------------------------
   PerfTop:   17064 irqs/sec  kernel:98.0% [100000 cycles],  (all, 4 CPUs)
------------------------------------------------------------------------------

             samples    pcnt   kernel function
             _______   _____   _______________

            40388.00 - 27.8% : acpi_idle_do_entry
            24651.00 - 17.0% : read_hpet
             4271.00 -  2.9% : _spin_lock
             3388.00 -  2.3% : pskb_expand_head
             3288.00 -  2.3% : igb_poll [igb]
             3246.00 -  2.2% : irq_entries_start
             2868.00 -  2.0% : dev_gro_receive
             2665.00 -  1.8% : igb_xmit_frame_adv       [igb]
             2513.00 -  1.7% : ip_route_input
             2144.00 -  1.5% : igb_clean_tx_irq [igb]
             1842.00 -  1.3% : __slab_free
             1544.00 -  1.1% : dev_queue_xmit
             1423.00 -  1.0% : igb_msix_rx      [igb]
             1353.00 -  0.9% : __alloc_skb
             1285.00 -  0.9% : eth_type_trans
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