Rutger Hofman wrote:
Hi list,
I have a board with an PXA270 and 32MB of flash, part of which is
configured as a jffs2 flash file system with Flash/v2 and legacy
interface. I also have language/C and many other C components configured
in, the relevant functions are open()/read() and fopen()/fread().
Now, if I read a file of size 503549 on this jffs2 file system, the
performance is *wildly* different for read() and fread():
file "/fpga/guardian_v3_rev_b.svf" size 503549
read file /fpga/guardian_v3_rev_b.svf size 503549 takes 0.863116
fread file /fpga/guardian_v3_rev_b.svf size 503549 takes 16.601978
Times are in seconds.
Question: why are the timings a factor of 20 apart? Why are the timings
different at all? I'd think that both do more or less exactly the same
thing, although at a different interface.
This provides at least part of the answer:
the data above were obtained with a buffer size of 8K. It appears that
FILEs have a buffer size of 256. If I change the buffer size in my test
program to 256, I get the following timings:
file "/fpga/guardian_v3_rev_b.svf" size 503549
read file /fpga/guardian_v3_rev_b.svf size 503549 takes 15.767474
fread file /fpga/guardian_v3_rev_b.svf size 503549 takes 16.624629
OK, so the difference all but disappears. So if I want to have some
performance in reading I'd better increase the FILE buffer size. I'll
check for setvbuf and friends.
Rutger Hofman
VU Amsterdam
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