Jim Gettys wrote: > On Mon, 2007-03-19 at 16:33 -0400, Bill Davidsen wrote: > > >> What you say sounds good, assuming that the cost of a sleep is less than >> the cost of the busy wait. But this may be hardware, the waits may be >> very small and frequent, and if it's hitting a small hardware window >> like retrace, delays in response will cause the time period to be missed >> completely. This probably less critical with very smart cards, many of >> us don't run them. >> > > Actually, various strategies involving short busy waiting, or looking at > DMA address registers before sleeping were commonplace. But a > syscall/sleep/wakeup is/was pretty fast. If you have an operation > blitting the screen (e.g. scrolling), it takes a bit of time for the GPU > to execute the command. I see this right now on OLPC, where a wonderful > music application needs to scroll (most of) the screen left), > periodically, and we're losing samples sometimes at those operation. > None of that conflicts with what I said, but what works on an LCD may not be appropriate for a CRT. With even moderate 1024x768@70 timing the horizontal retrace happens ~50k/sec, and that's not an appropriate syscall rate. I'm just pointing out that some things a video interface does with simple hardware involve lots of very small windows. Don't read that as "don't do it," just "be careful HOW you do it." > Remember also, that being nice to everyone else by sleeping, there are > more cycles to go around, and the scheduler can nicely boost the X > server's priority as it will for "interactive" processes that are being > cooperative. I'm going to cautiously guess that the problem might be not "how much" but "how soon." That is, latency might be more important than giving the server a lot of CPU. -- bill davidsen <davidsen@xxxxxxx> CTO TMR Associates, Inc Doing interesting things with small computers since 1979 _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
