PS Ram Speed

[shabtronic]

Hi Folks

I'm just venturing into using the 4mb PSRam on my esp32 board( currently a A1S - soon to be a Lyrat).

What read/write speeds should I be expecting?

I've written a simple test read program and I'm getting about 9MB/secs - that's single byte reads.

I'm just doing this so I can factor in any speed considerations for future projects.

thanks

Shabby

[ESP_Sprite]

There's a cache in front of the PSRAM (same as flash cache) so the numbers are a bit fuzzy, but in general the psram, if configured at 80MHz clock speed, should have some 40 MByte/sec throughput. Note that because a write goes through the cache, you probably will see half that: the cache line needs to be loaded from PSRAM on the first write and needs to be written back when the cache line is evicted. Note that all of this only applies if you process large (say, >16K) bits of data; small chunks will just stay in the cache and you'll get more-or-less the same speed as internal memory.

If you're getting 9MByte a second, you may want to set both your flash speed as well as your PSRAM speed to 80MHz (make menuconfig) as it sounds like those are set to 40MHz at the moment.

[shabtronic]

There's a cache in front of the PSRAM (same as flash cache) so the numbers are a bit fuzzy, but in general the psram, if configured at 80MHz clock speed, should have some 40 MByte/sec throughput. Note that because a write goes through the cache, you probably will see half that: the cache line needs to be loaded from PSRAM on the first write and needs to be written back when the cache line is evicted. Note that all of this only applies if you process large (say, >16K) bits of data; small chunks will just stay in the cache and you'll get more-or-less the same speed as internal memory.

If you're getting 9MByte a second, you may want to set both your flash speed as well as your PSRAM speed to 80MHz (make menuconfig) as it sounds like those are set to 40MHz at the moment.

Hi Esp_SPrite


thanks for taking the time to reply and the info - just wanted to know what to expect! 40mb/s that's great for a mmu/spi extension, beyond what I expected!

Shabby

[shabtronic]

Hi Folks

I put my mem speed test code and results on here - incase anyone else wants to try it - or spots any
errors in my code

I ran at 240mhz, spiram @ 80mhz

Ram Speed Test!

Read Speed 8bit ArraySize 1kb time: 0.0 22.6 mb/sec
Read Speed 8bit ArraySize 2kb time: 0.0 22.8 mb/sec
Read Speed 8bit ArraySize 4kb time: 0.0 22.8 mb/sec
Read Speed 8bit ArraySize 8kb time: 0.0 22.9 mb/sec
Read Speed 8bit ArraySize 16kb time: 0.0 22.9 mb/sec
Read Speed 8bit ArraySize 32kb time: 0.1 20.3 mb/sec
Read Speed 8bit ArraySize 64kb time: 0.3 12.0 mb/sec
Read Speed 8bit ArraySize 128kb time: 0.5 12.0 mb/sec
Read Speed 8bit ArraySize 256kb time: 1.0 12.0 mb/sec
Read Speed 8bit ArraySize 512kb time: 0.4 12.0 mb/sec
Read Speed 8bit ArraySize 1024kb time: 0.8 12.0 mb/sec
Read Speed 8bit ArraySize 2048kb time: 1.7 12.0 mb/sec
Read Speed 8bit ArraySize 4000kb time: 3.2 12.3 mb/sec

Read Speed 16bit ArraySize 1kb time: 0.0 45.3 mb/sec
Read Speed 16bit ArraySize 2kb time: 0.0 45.5 mb/sec
Read Speed 16bit ArraySize 4kb time: 0.0 45.6 mb/sec
Read Speed 16bit ArraySize 8kb time: 0.0 45.7 mb/sec
Read Speed 16bit ArraySize 16kb time: 0.0 45.7 mb/sec
Read Speed 16bit ArraySize 32kb time: 0.0 39.8 mb/sec
Read Speed 16bit ArraySize 64kb time: 0.2 17.0 mb/sec
Read Speed 16bit ArraySize 128kb time: 0.4 16.9 mb/sec
Read Speed 16bit ArraySize 256kb time: 0.7 16.9 mb/sec
Read Speed 16bit ArraySize 512kb time: 0.3 16.9 mb/sec
Read Speed 16bit ArraySize 1024kb time: 0.6 16.9 mb/sec
Read Speed 16bit ArraySize 2048kb time: 1.2 16.9 mb/sec
Read Speed 16bit ArraySize 4000kb time: 2.3 17.2 mb/sec

Read Speed 32bit ArraySize 1kb time: 0.0 89.6 mb/sec
Read Speed 32bit ArraySize 2kb time: 0.0 90.3 mb/sec
Read Speed 32bit ArraySize 4kb time: 0.0 91.0 mb/sec
Read Speed 32bit ArraySize 8kb time: 0.0 91.2 mb/sec
Read Speed 32bit ArraySize 16kb time: 0.0 91.4 mb/sec
Read Speed 32bit ArraySize 32kb time: 0.0 76.3 mb/sec
Read Speed 32bit ArraySize 64kb time: 0.1 21.2 mb/sec
Read Speed 32bit ArraySize 128kb time: 0.3 21.2 mb/sec
Read Speed 32bit ArraySize 256kb time: 0.6 21.2 mb/sec
Read Speed 32bit ArraySize 512kb time: 0.2 21.2 mb/sec
Read Speed 32bit ArraySize 1024kb time: 0.5 21.2 mb/sec
Read Speed 32bit ArraySize 2048kb time: 0.9 21.2 mb/sec
Read Speed 32bit ArraySize 4000kb time: 1.8 21.4 mb/sec
Test done!

Code: Select all

// Profile fun! microseconds to seconds
double GetTime() { return (double)esp_timer_get_time() / 1000000; }

int RamTest()
	{
	int rs[] = { 1,2,4,8,16,32,64,128,256,512,1024,2048,4000 };
	printf("Ram Speed Test!\n\n");
	char xx = 0;
	for (int a = 0; a < 13; a++)
		{
		printf("Read Speed 8bit ArraySize %4dkb ", rs[a]);
		int ramsize = rs[a] * 1024;
		char * rm = (char*)malloc(ramsize);

		int iters = 10; // Just enuff to boot the dog
		if (rs[a] < 512) iters = 50;
		double st = GetTime();
		for (int b = 0; b < iters; b++)
			for (int c = 0; c < ramsize; c++)
				xx |= rm[c];
		st = GetTime() - st;
		vTaskDelay(1); // Dog it!
		double speed = ((double)(iters*ramsize ) / (1024 * 1024)) / (st);
		printf(" time: %2.1f %2.1f mb/sec  \n", st, speed);
		free(rm);
		}
	printf("\n");
	for (int a = 0; a < 13; a++)
		{
		printf("Read Speed 16bit ArraySize %4dkb ", rs[a]);
		int ramsize = rs[a] * 1024;
		short * rm = (short*)malloc(ramsize);

		int iters = 10; // Just enuff to boot the dog
		if (rs[a] < 512) iters = 50;
		double st = GetTime();
		for (int b = 0; b < iters; b++)
			for (int c = 0; c < ramsize/2; c++)
				xx |= rm[c];
		st = GetTime() - st;
		vTaskDelay(1); // Dog it!
		double speed = ((double)(iters*ramsize) / (1024 * 1024)) / (st);
		printf(" time: %2.1f %2.1f mb/sec  \n", st, speed);
		free(rm);
		}
	printf("\n");
	for (int a = 0; a < 13; a++)
		{
		printf("Read Speed 32bit ArraySize %4dkb ", rs[a]);
		int ramsize = rs[a] * 1024;
		int * rm = (int*)malloc(ramsize);

		int iters = 10; // Just enuff to boot the dog
		if (rs[a] < 512) iters = 50;
		double st = GetTime();
		for (int b = 0; b < iters; b++)
			for (int c = 0; c < ramsize/4; c++)
				xx |= rm[c];
		st = GetTime() - st;
		vTaskDelay(1); // Dog it!
		double speed = ((double)(iters*ramsize) / (1024 * 1024)) / (st);
		printf(" time: %2.1f %2.1f mb/sec  \n", st, speed);
		free(rm);
		}
	printf("Test done!\n");
	return xx;
	}

[ESP_Sprite]

Those results are more or less what I'd expect. For lower array sizes, the array is entirely kept in cache and the speed is however fast the CPU can write there; you can see that because 8-bit writes are less efficient than 32-bit writes. From 16K'ish, the array can't be contained in the cache anymore and the performance slowly degrades to the theoretical 20MByte/sec read-modify-write speeds of the psram itself.

[shabtronic]

Those results are more or less what I'd expect. For lower array sizes, the array is entirely kept in cache and the speed is however fast the CPU can write there; you can see that because 8-bit writes are less efficient than 32-bit writes. From 16K'ish, the array can't be contained in the cache anymore and the performance slowly degrades to the theoretical 20MByte/sec read-modify-write speeds of the psram itself.

Hi ESP_Sprite

Yeah - I noticed the cache thrash around 32kb. I'm super chuffed with these results - it makes
a whole bundle of projects feasible for me - yaaay!!!

Shabby

[franzhoepfinger]

char * rm = (char*)malloc(ramsize);
should be replaced by
char * rm = (char*)heap_caps_malloc(ramsize, MALLOC_CAP_SPIRAM);

[zekageri]

So it took 1.8 sec to read 4mb?

[ghost07]

Yeah, read 4MB in 1.8 sec seems more like 2.14MB/sec, not 21.4MB/sec.
However, after checking the code, he ran 10 iterations, so he actually read 40MB in 1.8 sec, and that would give 21.4 MB/sec.
Just saying for future confused visitors.