Hi,
On Wednesday, 17 January 2007 23:03, Michal Schmidt wrote:
> Pavel Machek wrote:
> > Hi!
> >
> >> writing the image to disk wastes 10 seconds by waiting for 0.1s a
> >> hundred times.
> >
> > Are you sure?
>
> In practice the real slowdown is less than 10s, because the disk is
> usually writing while key_pressed() is waiting. If you had a very fast
> disk, the slowdown would become more noticeable. I actually tried
> commenting out the call to swap_write_page from the loop in save_image
> and the loop still took 10s to run. With my patch it executes almost
> instantly.
>
> >> The problem is the key_pressed function. It always attempts to read a
> >> char from the terminal with a timeout of 1 decisecond. It's better to
> >> poll the terminal without unnecessary waiting.
> >>
> >> On my laptop the improvement is very noticeable if I enable compression.
> >> With compression disabled, the effect is not so obvious, because disk
> >> throughput is the bottleneck.
> >
> >> @@ -54,6 +52,14 @@
> >> static int key_pressed(const char key)
> >> {
> >> char c;
> >> + fd_set fds;
> >> + struct timeval tv = {0, 0};
> >> +
> >> + FD_ZERO(&fds);
> >> + FD_SET(0, &fds);
> >> + if (select(1, &fds, NULL, NULL, &tv) <= 0)
> >> + return 0;
> >> +
> >> if (read(0, &c, 1) > 0 && c == key)
> >> return 1;
> >
> >
> > That seems unneccessarily complex, just set stdin to nonblocking mode
> > and read should return immediately, right?
> > Pavel
>
> Right. Here's a much simpler patch with the same effect.
I think this one is simple enough so that we can apply it. :-) Pavel?
--
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you don't have the time or the tools to write.
- Stephen King
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