On Wed 2009-03-04 15:00:01, Uli Luckas wrote: > On Tuesday, 3. March 2009, Pavel Machek wrote: > > Hi! > > > > > > > > And introduce nasty interface, and probably slower too since open() > > > > > > is time-critical and ioctl() is not? Or do you have benchmarks? > > > > > > > > > > No, just specualting as open() needs to do a directory lookup. It > > > > > also needs to do book keeping. I'd be surprised if open was faster > > > > > then ioctl. > > > > > > > > Unless you measure how much slower it is... > > > > > > OK. Opening /dev/null 100000 times readonly takes 365 ms on my machine. > > > Opening it once and then, 100000 times writing 1 byte takes 32 ms. > > > Why exactly did you think I had to provide numbers??? > > > > Arve said: > > > >> I just checked my phone, and over a 24 hour awake time (370 hours > > > >> uptime) period, it acquired about 5 million wakelocks (mostly for > > > >> input events). If these were cache hits, and took as long as my > > > >> benchmark did, that accounts for 20 seconds of overhead (0.023% > > > >> of > > > >> awake, 0.1% of not-idle (5.5h). > > > > Ok. 20seconds vs. 200 seconds seems interesting. > > > > OTOH... Android seems to do IPC for wakelock manipulation, and that's > > way higher overhead than open() syscall, so perhaps it is not that > > critical? > > > Is IPC (writing a byte through a pipe/socket) really more expensive than > open/close? Given that on current android it is "send a byte to another process that does open/write/close"... yes that looks more expensive than single open. > here is network packets. You just don't want to open/close a fd for every > network packet that you process. Neither for serial data, bluetooth > packets, ... You mix userland and kernel users. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
