On 12/10/06, Linus Torvalds <torvalds@xxxxxxxx> wrote:
On Sun, 10 Dec 2006, Marco Costalba wrote: > > Ok. Perhaps I'm doing something wrong but the following code it's > always 10% slower then the temporary file one (4.7s against 4.3s for > linux tree) Why do you seem to be doing a "new" on every iteration inside the loop?
Becuase it's there where I store the file content. Function parseSingleBuffer(ba) does only the indexing. But the file content is stored in QByteArray objects (little wrappers around a const char* []). So the fread() in the byte array object is the _only_ data copy operation in whole qgit.
Also, why do you have that strange FILE_BLOCK_SIZE thing, and in particular the "if (len < FILE_BLOCK_SIZE)" check? One thing that pipes vs files do is the blocking factor. Especially with older kernels, I _guarantee_ you that you'll only ever get 4kB at a time, so because of that "if (len < 64kB) break" thing, the only thing you're doing is to make sure things suck performance-wise, and you won't be reading the rest of the data until 100ms later.
I consistently have len == 65536 bytes until the last fread() where it's less. See below run against qgit own repository with 'len' printed inside while loop. $ ./qgit Found GNU source-highlight 2.5 len is <65536> len is <65536> len is <65536> len is <65536> len is <65536> len is <65536> len is <65536> len is <54479> bash-3.1$
IOW, your code is written for a file, and makes no sense there either (checking "feof(file)" is wrong, since you may well have hit the EOF *at*that*time*, but the file may GROW since you are doing it all in the background, so you can't rely on feof() anyway).
Yes. feof() it's difficult to handle correctly.
For a pipe, what you should do is to make sure it's in nonblocking mode, and just continue reading until it gets no more. And instead of using a timeout, you should use poll() or something to get notified when there is more data.
How can open in nonblocking mode with popen() ? FILE *popen(const char *command, const char *type);
IOW, the reason it's slow is because you're doing the wrong thing.
That's for sure :-) My problem is to guess what's is wrong. Marco - To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html