On Thu 2007-01-18 00:13:54, Rafael J. Wysocki wrote:
> 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?
Ack, go ahead.
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures)
http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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