This post is an extension to my earlier query regarding read() and write() time.
To avoid confusions, I am posting a new topic in a different context.
Please note: Before reading this thread, if you want to refer my earlier queries and replies, please refer
openqnx.com/phpbbforum/viewt … 10&t=13551
I am still trying to get a solution for getting the actual read(), write() speed without involving system cache to the maximum.
Problem is getting worse when I do a read() after a write() and a simple read() alone to the disk.
read() after a write() is very faster than read() alone.
I have tried one more approach. I have given cache=0M argument to devb-eide driver at bootup.
Then speed of read() after write() for MB sized blocks is almost comparable to read() alone speed.
But for smaller KB sized blocks, speed variation still exists.
But I am not sure of the root cause of this speed variation at smaller data sizes.
Also I am not sure what this “cache=” argument means for devb-eide? Is it disk cache or system cache?
Is it a good way to disable cache to 0M?
On just skimming through QNX help files, I again noticed another set of functions like msync(), mmap_device_memory,
cache_init(), CACHE_FLUSH() and CACHE_INVAL().
Could any one please comment on whether I can use any combinations of these routines to measure the actual speed of my read(),
Note: For the time-being, we can ignore the usecase of disabling disk cache. Just consider disabling the system cache.
I would like to experiment on how disabling system caching will affect the usecase…
Please also share if you have any other ideas on this problem…
I am very much stuck in this issue…