On Sun, 2005-03-27 at 10:58 +0200, Ingo Molnar wrote: > * Lee Revell <[EMAIL PROTECTED]> wrote: > > > Running for several days with PREEMPT_DESKTOP, on the Athlon XP the > > worst latency I am seeing is ~150 usecs! But on the C3 its about 4ms: > > could you run a bit with tracing disabled (in the .config) on the C3? > (but wakeup timing still enabled) It may very well be tracing overhead > that makes those latencies that high. Also, we'd thus have some hard > data on how much overhead tracing is in such a situation, on that CPU. >
I have not left it to run overnight yet with the swappiness set to 100, which triggers the biggest latencies as my entire desktop is swapped out, but so far it looks like the problem was tracing overhead. With timing enabled but tracing disabled the longest latency on the C3 so far is 270 usecs. An important giveaway is that with tracing enabled the same code path only triggers ~200 usec latencies on the K7 but ~2ms on the C3. Since the longest latency with PREEMPT_DESKTOP is normally more a function of memory bandwidth than processor speed, and the machines differ much more in the latter, this agrees with the theory that the overhead is the problem. Lee - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/