On 10/14/2010 07:57 PM, Denis Koroskin wrote:
In my original version there was a setbuf(f, null) call. I removed it because it had 0 impact on performance. I also tried using unistd open/read functions, that had zero impact, too
Yah, I looked more into the behavior of fread. At least on a couple of implementations that offer source, the implementation first copies whatever data is (if any) in the internal buffer, and then read the rest of the data straight into the remaining user-supplied buffer.
This means, if you consistently fread into a buffer, the internal buffers are never touched.
I stand corrected regarding the extra copy.
(btw, opening file with O_DIRECT returned valid file descriptor, but read operations very failing with an invalid argument error).
I recall I've read a discussion where Linus was really down on O_DIRECT. Found it: http://kerneltrap.org/node/7563
Andrei
