Warning when running LWFA example

[denisbertini]

Hi
I got this kind of warning when running LWFA from examples directory

Performance warning: send/receive buffer for species e is too small (max: 65536, direction: 6 'top', retries: 1). To remove this warning consider increasing BYTES_EXCHANGE_{X,Y,Z} in memory.param

what part has to be increased ( i am using the default 32 bit precision )

 struct DefaultExchangeMemCfg
    {
        // Memory used for a direction for a simulation performed with 32bit precision.
        static constexpr uint32_t BYTES_EXCHANGE_X = 1 * 1024 * 1024; // 1 MiB
        static constexpr uint32_t BYTES_EXCHANGE_Y = 3 * 1024 * 1024; // 3 MiB
        static constexpr uint32_t BYTES_EXCHANGE_Z = 1 * 1024 * 1024; // 1 MiB
        static constexpr uint32_t BYTES_EDGES = 32 * 1024; // 32 kiB
        static constexpr uint32_t BYTES_CORNER = 8 * 1024; // 8 kiB

How direction 6, top map to direction ?
Should i increase on X , Y, Z or all items and how much ( 2 x ) ?

[psychocoderHPC]

Note: It is only a warning and will slow down your code, the results should not be affected by this.

To solve the issue, you can as you said increase the memory for the corresponding direction.

 (max: 65536, direction: 6 'top', retries: 1)

How to read this?

• direction: 6 'top' -> is the y direction, so many particles in your simulation flow into Y direction, This is what you should increase
• retries: 1 -> means that PIConGPU was required to repeat the sending process once to communicate all particles. If you increase Y by a factor 2 the issues should be solved. Depending on your dynamics in later timesteps this message can be shown again.

Short

This should solve your issue

static constexpr uint32_t BYTES_EXCHANGE_Y = 3 * 1024 * 1024 * 2; // 6 MiB

[psychocoderHPC]

PIConGPU coordinate system:

picongpu/include/pmacc/type/Exchange.hpp

Lines 40 to 44 in 4893347

	* Axis index relation:
	* right & left are in X
	* bottom & top are in Y
	* back & front are in Z
	*/

[denisbertini]

thanks a lot !

[PrometheusPi]

@denisbertini If this answers your question, please feel free to close this issue.

[denisbertini]

well i actually tried that, but then the other problem with the options ambiguous arised again. and then put back the initial
memory layout and ... works fine again but with the warning as expected .
So some memory issue?

[psychocoderHPC]

Changing the memory size should not produce your mutiple option issue.

[PrometheusPi]

So this performance issue and the multi-plugin issue #5564 are related for you?