Le mardi 27 mars 2007 à 17:13 -0600, Hans Petter Jansson a écrit : > On Wed, 2007-03-28 at 00:28 +0200, Xavier Bestel wrote: > > On mar, 2007-03-27 at 14:52 -0600, Federico Mena Quintero wrote: > > > > [/me wonders if thumbnailers are measurably faster by using mmap() > > > instead of read()...] > > > It depends on their access pattern. If they need sequential access, > > read() is better because it can do prefetching (readahead). > > I think what Federico was getting at is that for most thumbnailers, > rendering is likely to be a bigger bottleneck than I/O on a local file > system. But we don't know this for sure until we've measured it.
Linus seems to agree with you wrt real-world testing: http://gcc.gnu.org/ml/gcc-patches/2001-09/msg00358.html > mmap() can do prefetching too - and it will likely load a 4k page at a > time anyway. So I doubt prefetch plays a role in a comparison of read() > and mmap(). > > I tend to favor read() on user data: > > - For robustness: An mmap() map can become invalid if the file is > truncated, crashing the process. > - Because mmap() makes your VSize - and with accesses, your RSS - grow > correspondingly, with subsequent bug reports from irate users. Sure. Xav _______________________________________________ desktop-devel-list mailing list desktop-devel-list@gnome.org http://mail.gnome.org/mailman/listinfo/desktop-devel-list