Timer coalescing works on the assumption that most drivers and user-mode applications do not particularly care about the exact firing period of their timers (except in the case of multimedia applications, for example). This “don’t care” region actually grows as the original timer period grows—an application waking up every 30 seconds probably doesn’t mind waking up every 31 or 29 seconds instead, while a driver polling every second could probably poll every second plus or minus 50 ms without too many problems. The important guarantee most periodic timers depend on is that their firing period remains constant within a certain range—for example, when a timer has been changed to fire every second plus 50 ms, it continues to fire within that range forever, not sometimes at every two seconds and other times at half a second. Even so, not all timers are ready to be coalesced into coarser granularities, so Windows enables this mechanism only for timers that have marked themselves as coalescable, either through the
With these APIs, driver and application developers are free to provide the kernel with the maximum
When a tolerable delay is set for a periodic timer, Windows uses a process called
Now with timer coalescing, refer back to Figure 3-11 and assume all the timers specified tolerances and are thus coalescable. In one scenario, Windows could decide to coalesce the timers as shown in Figure 3-12. Notice that now, processor 1 receives a total of only three clock interrupts, significantly increasing the periods of idle sleep, thus achieving a lower C-state. Furthermore, there is less work to do for some of the clock interrupts on processor 0, possibly removing the latency of requiring a drop to DISPATCH_LEVEL at each clock interrupt.
Exception Dispatching
In contrast to interrupts, which can occur at any time, exceptions are conditions that result directly from the execution of the program that is running. Windows uses a facility known as
Вильям Л Саймон , Вильям Саймон , Наталья Владимировна Макеева , Нора Робертс , Юрий Викторович Щербатых
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