Re: [PATCH] -mm: i386 apm.c optimization

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Andreas Mohr wrote:

Hello all,

- avoid expensive modulo (integer division) which happened
 since APM_MAX_EVENTS is 20 (non-power-of-2)
- kill compiler warnings by initializing two variables
- add __read_mostly to some important static variables that are read often
 (by idle loop etc.)
- constify several structures

Patch tested on 2.6.16-ck5, rediffed against 2.6.17-rc1-mm2. @@ -1104,7 +1105,8 @@

static apm_event_t get_queued_event(struct apm_user *as)
{
-	as->event_tail = (as->event_tail + 1) % APM_MAX_EVENTS;
+	if (++as->event_tail >= APM_MAX_EVENTS)
+		as->event_tail = 0;
	return as->events[as->event_tail];
}

Either event_tail can never be > APM_MAX_EVENTS (I believe that's true) and you should use ==, or you should do a proper mod function:
 ++as->event_tail;
 while (as->event_tail >= APM_MAX_EVENTS) as->event_tail -= APM_MAX_EVENTS;

In the unlikely even that the event_tail is already too large you want a proper mod, not to set it to zero.

--
bill davidsen <davidsen@xxxxxxx>
 CTO TMR Associates, Inc
 Doing interesting things with small computers since 1979

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