Messages in this thread | | | Date | Fri, 12 Aug 2011 13:45:28 +0800 | From | Wu Fengguang <> | Subject | Re: [PATCH 2/5] writeback: dirty position control |
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> > Making our final function look like: > > > > s - x 3 > > f(x) := 1 + (-----) > > l - s > > Very intuitive reasoning, thanks! > > I substituted real numbers to the function assuming a mem=2GB system. > > with limit=thresh: > > gnuplot> set xrange [60000:80000] > gnuplot> plot 1 + (70000.0 - x)**3/(80000-70000.0)**3
I'll use the above one, which is more simple and elegant:
f(freerun) = 2.0 f(setpoint) = 1.0 f(limit) = 0
Code is
unsigned long freerun = (thresh + bg_thresh) / 2;
setpoint = (limit + freerun) / 2; pos_ratio = abs(dirty - setpoint); pos_ratio <<= BANDWIDTH_CALC_SHIFT; do_div(pos_ratio, limit - setpoint + 1); x = pos_ratio; pos_ratio = pos_ratio * x >> BANDWIDTH_CALC_SHIFT; pos_ratio = pos_ratio * x >> BANDWIDTH_CALC_SHIFT; if (dirty > setpoint) pos_ratio = -pos_ratio; pos_ratio += 1 << BANDWIDTH_CALC_SHIFT;
Thanks, Fengguang
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