Stefan Monnier wrote on 05/11/2019 03:37 PM:
Increasing the SATA/AHCI DMA TX/RX FIFOs (P0DMACR.TXTS and .RXTS) from default 0x0 each to 0x3 each gives a write performance boost of 120MB/s from lame 36MB/s to 45MB/s previously. Read performance is about 200MB/s [tested on SSD using dd bs=4K count=512K].
Such a simple patch to fix such a long-standing performance problem that everyone [ well, apparently not quite everyone ] assumed was a hardware limitation...
And yet, April 1st is long gone.
Is it really for real?
Yes, it's indeed real, Stefan; really no April 1st joke. :-)
As you indicated, this problem of slow SATA write-speed with these small devices lasts now for more than 5 years. This patch finally solves the problem.
On my test device (BPI-R1) the optimum blocksize seems to be 12K as it then gives even 129 MB/s write speed.
Here are some test results with different blocksizes, all giving a write speed of 125 to 129 MB/s:
time sh -c "dd if=/dev/zero of=test.tmp bs=$bs count=$count conv=fdatasync"
------------ bs=8K / count=256K / 1 ------------------ 262144+0 records in 262144+0 records out 2147483648 bytes (2.1 GB) copied, 16.9237 s, 127 MB/s
real 0m16.935s user 0m0.388s sys 0m15.777s
------------ bs=8K / count=256K / 2 ------------------ 262144+0 records in 262144+0 records out 2147483648 bytes (2.1 GB) copied, 16.9916 s, 126 MB/s
real 0m17.973s user 0m0.326s sys 0m16.806s
------------ bs=8K / count=256K / 3 ------------------ 262144+0 records in 262144+0 records out 2147483648 bytes (2.1 GB) copied, 17.0085 s, 126 MB/s
real 0m17.993s user 0m0.442s sys 0m16.588s
------------ bs=12K / count=171K / 1 ------------------ 175104+0 records in 175104+0 records out 2151677952 bytes (2.2 GB) copied, 16.8474 s, 128 MB/s
real 0m16.860s user 0m0.205s sys 0m15.705s
------------ bs=12K / count=171K / 2 ------------------ 175104+0 records in 175104+0 records out 2151677952 bytes (2.2 GB) copied, 16.6934 s, 129 MB/s
real 0m17.669s user 0m0.227s sys 0m16.355s
------------ bs=12K / count=171K / 3 ------------------ 175104+0 records in 175104+0 records out 2151677952 bytes (2.2 GB) copied, 16.6684 s, 129 MB/s
real 0m17.654s user 0m0.388s sys 0m16.118s
------------ bs=16K / count=128K / 1 ------------------ 131072+0 records in 131072+0 records out 2147483648 bytes (2.1 GB) copied, 17.1845 s, 125 MB/s
real 0m17.200s user 0m0.251s sys 0m16.060s
------------ bs=16K / count=128K / 2 ------------------ 131072+0 records in 131072+0 records out 2147483648 bytes (2.1 GB) copied, 16.9221 s, 127 MB/s
real 0m17.902s user 0m0.170s sys 0m16.763s
------------ bs=16K / count=128K / 3 ------------------ 131072+0 records in 131072+0 records out 2147483648 bytes (2.1 GB) copied, 16.8845 s, 127 MB/s
real 0m17.868s user 0m0.167s sys 0m16.736s