Re: [dpdk-dev] [PATCH v2] ethdev: make struct rte_eth_dev cache aligned

[Jerin Jacob <jerin.jacob@caviumnetworks.com>]

On Wed, May 04, 2016 at 12:09:50PM +0100, Bruce Richardson wrote:
> On Tue, May 03, 2016 at 06:12:07PM +0530, Jerin Jacob wrote:
> > Elements of struct rte_eth_dev used in the fast path.
> > Make struct rte_eth_dev cache aligned to avoid the cases where
> > rte_eth_dev elements share the same cache line with other structures.
> > 
> > Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> > ---
> > v2:
> > Remove __rte_cache_aligned from rte_eth_devices and keep
> > it only at struct rte_eth_dev definition as suggested by Bruce
> > http://dpdk.org/dev/patchwork/patch/12328/
> > ---
> >  lib/librte_ether/rte_ethdev.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/lib/librte_ether/rte_ethdev.h b/lib/librte_ether/rte_ethdev.h
> > index 2757510..48f14d5 100644
> > --- a/lib/librte_ether/rte_ethdev.h
> > +++ b/lib/librte_ether/rte_ethdev.h
> > @@ -1615,7 +1615,7 @@ struct rte_eth_dev {
> >  	struct rte_eth_rxtx_callback *pre_tx_burst_cbs[RTE_MAX_QUEUES_PER_PORT];
> >  	uint8_t attached; /**< Flag indicating the port is attached */
> >  	enum rte_eth_dev_type dev_type; /**< Flag indicating the device type */
> > -};
> > +} __rte_cache_aligned;
> >  
> >  struct rte_eth_dev_sriov {
> >  	uint8_t active;               /**< SRIOV is active with 16, 32 or 64 pools */
> > -- 
> 
> Hi Jerin,

Hi Bruce,

> 
> have you seen a performance degradation due to ethdev elements sharing a cache

No. Not because of sharing the cache line.

> line? I ask because, surprisingly for me, I actually see a performance regression

I see performance degradation in PMD in my setup where independent
changes are causing the performance issue in PMD(~<100k). That's the reason
I thought making aligned cache line stuff where ever it makes sense so that
independent change shouldn't impact the PMD performance and this patch
was an initiative for the same.

> when I apply the above patch. It's not a big change - perf reduction of <1% - but
> still noticable across multiple runs using testpmd. I'm using two 1x40G NICs
> using i40e driver, and I see ~100kpps less traffic per port after applying the
> patch. [CPU: Intel(R) Xeon(R) CPU E5-2699 v3 @ 2.30GHz]

This particular patch does not have any performance degradation in my
setup.
CPU: ThunderX

> 
> Testpmd cmd and output shown below.
> 
> Regards,
> /Bruce
> 
> $ sudo ./x86_64-native-linuxapp-gcc/app/testpmd -c C0000 -n 4 -- --rxd=512 --txd=512 --numa
> EAL: Detected 36 lcore(s)
> EAL: Probing VFIO support...
> PMD: nfp_net_pmd_init(): librte_pmd_nfp_net version 0.1
> 
> EAL: PCI device 0000:01:00.0 on NUMA socket 0
> EAL:   probe driver: 8086:1521 rte_igb_pmd
> EAL: PCI device 0000:01:00.1 on NUMA socket 0
> EAL:   probe driver: 8086:1521 rte_igb_pmd
> EAL: PCI device 0000:05:00.0 on NUMA socket 0
> EAL:   probe driver: 8086:154a rte_ixgbe_pmd
> EAL: PCI device 0000:05:00.1 on NUMA socket 0
> EAL:   probe driver: 8086:154a rte_ixgbe_pmd
> EAL: PCI device 0000:08:00.0 on NUMA socket 0
> EAL:   probe driver: 8086:154a rte_ixgbe_pmd
> EAL: PCI device 0000:08:00.1 on NUMA socket 0
> EAL:   probe driver: 8086:154a rte_ixgbe_pmd
> EAL: PCI device 0000:81:00.0 on NUMA socket 1
> EAL:   probe driver: 8086:1584 rte_i40e_pmd
> PMD: eth_i40e_dev_init(): FW 5.0 API 1.5 NVM 05.00.02 eetrack 80002281
> EAL: PCI device 0000:88:00.0 on NUMA socket 1
> EAL:   probe driver: 8086:1584 rte_i40e_pmd
> PMD: eth_i40e_dev_init(): FW 5.0 API 1.5 NVM 05.00.02 eetrack 80002281
> Configuring Port 0 (socket 1)
> Port 0: 68:05:CA:27:D4:4E
> Configuring Port 1 (socket 1)
> Port 1: 68:05:CA:27:D2:0A
> Checking link statuses...
> Port 0 Link Up - speed 40000 Mbps - full-duplex
> Port 1 Link Up - speed 40000 Mbps - full-duplex
> Done
> No commandline core given, start packet forwarding
>   io packet forwarding - CRC stripping disabled - packets/burst=32
>   nb forwarding cores=1 - nb forwarding ports=2
>   RX queues=1 - RX desc=512 - RX free threshold=32
>   RX threshold registers: pthresh=8 hthresh=8 wthresh=0
>   TX queues=1 - TX desc=512 - TX free threshold=32
>   TX threshold registers: pthresh=32 hthresh=0 wthresh=0
>   TX RS bit threshold=32 - TXQ flags=0xf01
> Press enter to exit
> 
> Telling cores to stop...
> Waiting for lcores to finish...
> 
>   ---------------------- Forward statistics for port 0  ----------------------
>   RX-packets: 1940564672     RX-dropped: 1456035742    RX-total: 3396600414
>   TX-packets: 1940564736     TX-dropped: 0             TX-total: 1940564736
>   ----------------------------------------------------------------------------
> 
>   ---------------------- Forward statistics for port 1  ----------------------
>   RX-packets: 1940564671     RX-dropped: 1456036082    RX-total: 3396600753
>   TX-packets: 1940564736     TX-dropped: 0             TX-total: 1940564736
>   ----------------------------------------------------------------------------
> 
>   +++++++++++++++ Accumulated forward statistics for all ports+++++++++++++++
>   RX-packets: 3881129343     RX-dropped: 2912071824    RX-total: 6793201167
>   TX-packets: 3881129472     TX-dropped: 0             TX-total: 3881129472
>   ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 
> Done.
> 
> Shutting down port 0...
> Stopping ports...
> Done
> Closing ports...
> Done
> 
> Shutting down port 1...
> Stopping ports...
> Done
> Closing ports...
> Done
> 
> Bye...
> 
>