Hi, On Sun, Jun 10, 2007 at 09:44:05AM -0000, Thomas Gleixner wrote: > From: john stultz <[EMAIL PROTECTED]> > > After discussing w/ Thomas over IRC, it seems the issue is the sched > tick fires on every cpu at the same time, causing extra lock contention.
Hmm, the cpu-specific offset calculation isn't too expensive, hopefully? (div/mul in patch, maybe this could be done differently) And is it granted that the do_div() compiles into a nice plain void on non-SMP? Would be good to verify this. And calculation order? Do multiply before division to minimize calculation error? (for a timer tick it probably doesn't matter, however) And of course OTOH doing it the other way might lead to overflows... > This smaller change, adds an extra offset per cpu so the ticks don't > line up. This patch also drops the idle latency from 40us down to under > 20us. Very nice, thanks! > + /* Get the next period (per cpu)*/ > ts->sched_timer.expires = tick_init_jiffy_update(); > + offset = ktime_to_ns(tick_period) >> 1; > + do_div(offset, NR_CPUS); > + offset *= smp_processor_id(); Andreas Mohr - 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/
