On Wed, Jun 20, 2012, at 03:06 PM, Arnd Bergmann wrote:
On Wednesday 20 June 2012, Andrew Bradford wrote:
[andrew@mythdvr flashbench]$ sudo ./flashbench /dev/sdb --open-au --erasesize=$[8*1024*1024] --blocksize=$[16*1024] --open-au-nr=4 --offset=$[23*1024*1024] 8MiB 32.7M/s 4MiB 12.9M/s 2MiB 20.9M/s 1MiB 6.4M/s 512KiB 19.6M/s 256KiB 4.14M/s 128KiB 23.8M/s 64KiB 2.88M/s 32KiB 8.76M/s 16KiB 1.72M/s
24MiB definitely looking like a boundary. At the smaller blocksizes, it looks as though alignment with the erase block isn't what causes the slowness. On the bigger sizes, alignment definitely is important. Would this indicate anything in particular about the garbage collection routines? Or any other activities of the controller?
One thing I notice here is that ever other row is slow, so you get into garbage collection only sometimes in the 4*8MB test case, and that is the same for 4*3MB.
OK.
The trick that I sometimes use when finding out the erase block size is as hard as with this one is to try all sorts of boundaries. Given that the 25 MB offset is not slower than the 24 MB one for 3 MB erase blocks, I would guess that the erase size has to be larger than 3 MB. The question to look at really is how far you have to move the offset until you hit the next boundary after 24 MB.
I'm having trouble reproducing my tests from yesterday, for example (same as above at 23MiB offset) but now without the fast-slow-fast-slow lines:
[andrew@mythdvr flashbench]$ sudo ./flashbench /dev/sdb --open-au --erasesize=$[8*1024*1024] --blocksize=$[16*1024] --open-au-nr=4 --offset=$[23*1024*1204] 8MiB 8.75M/s 4MiB 8.24M/s 2MiB 6.82M/s 1MiB 4.61M/s 512KiB 4.83M/s 256KiB 5.29M/s 128KiB 4.71M/s 64KiB 3.46M/s 32KiB 2.79M/s 16KiB 1.07M/s
I can consistently reproduce this type of performance, but I can't get back to the fast-slow-fast-slow lines performance. Which makes me question the validity of all my other tests.
Is there any reason why I'd see so much variability between running the same test on the same machine one day to the next? I even rebooted this morning but still can't get back to the fast-slow-fast-slow lines. I can't remember seeing this much difference one day to the next with the SD cards I've tested, they seemed pretty consistent.
I don't feel confident comparing one day's measurements to another's and making valid conclusions if I can't reproduce the previous results.
Thanks for your help! -Andrew