Messages in this thread | | | Date | Mon, 18 Jun 2012 18:06:18 +0800 | From | Charles Wang <> | Subject | Re: [PATCH] sched: Folding nohz load accounting more accurate |
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On Saturday, June 16, 2012 01:39 AM, Peter Zijlstra wrote:
> Wednesday I ended up with something like the below.. but I haven't > gotten round to trying Doug's latest testing method, nor did I really > read the email I'm now replying to. > > I think it does something like what Wang described... every time I try > and write comments related to why it does this I get stuck though. > > I ran out of time again for this week, I'll try and prod at it a little > more next week (and try and catch up with the thread). > > In the meantime I thought I might as well post this.. who knows somebody > might be bored over the weekend, it might actually work, or not :-) > > --- > kernel/sched/core.c | 77 +++++++++++++++++++++++++++++++++++---------------- > 1 file changed, 53 insertions(+), 24 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index ca07ee0..4101a0e 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2198,26 +2198,49 @@ calc_load(unsigned long load, unsigned long exp, unsigned long active) > * > * When making the ILB scale, we should try to pull this in as well. > */ > -static atomic_long_t calc_load_tasks_idle; > +static atomic_long_t calc_load_idle[2]; > +static int calc_load_idx; > + > +static inline int calc_load_write_idx(void) > +{ > + int idx = calc_load_idx; > + > + /* > + * See calc_global_nohz(), if we observe the new index, we also > + * need to observe the new update time. > + */ > + smp_rmb(); > + > + if (!time_before(jiffies, calc_load_update)) > + idx++; > + > + return idx & 1; > +} > + > +static inline int calc_load_read_idx(void) > +{ > + return calc_load_idx & 1; > +} > > void calc_load_account_idle(struct rq *this_rq) > { > long delta; > + int idx; > > delta = calc_load_fold_active(this_rq); > - if (delta) > - atomic_long_add(delta, &calc_load_tasks_idle); > + if (delta) { > + idx = calc_load_write_idx(); > + atomic_long_add(delta, &calc_load_idle[idx]); > + } > } > > static long calc_load_fold_idle(void) > { > + int idx = calc_load_read_idx(); > long delta = 0; > > - /* > - * Its got a race, we don't care... > - */ > - if (atomic_long_read(&calc_load_tasks_idle)) > - delta = atomic_long_xchg(&calc_load_tasks_idle, 0); > + if (atomic_long_read(&calc_load_idle[idx])) > + delta = atomic_long_xchg(&calc_load_idle[idx], 0); > > return delta; > } > @@ -2313,26 +2336,32 @@ static void calc_global_nohz(void) > if (delta) > atomic_long_add(delta, &calc_load_tasks); > > - /* > - * It could be the one fold was all it took, we done! > - */ > - if (time_before(jiffies, calc_load_update + 10)) > - return; > + if (!time_before(jiffies, calc_load_update + 10)) { > + /* > + * Catch-up, fold however many we are behind still > + */ > + delta = jiffies - calc_load_update - 10; > + n = 1 + (delta / LOAD_FREQ); > > - /* > - * Catch-up, fold however many we are behind still > - */ > - delta = jiffies - calc_load_update - 10; > - n = 1 + (delta / LOAD_FREQ); > + active = atomic_long_read(&calc_load_tasks); > + active = active > 0 ? active * FIXED_1 : 0; > > - active = atomic_long_read(&calc_load_tasks); > - active = active > 0 ? active * FIXED_1 : 0; > + avenrun[0] = calc_load_n(avenrun[0], EXP_1, active, n); > + avenrun[1] = calc_load_n(avenrun[1], EXP_5, active, n); > + avenrun[2] = calc_load_n(avenrun[2], EXP_15, active, n); > > - avenrun[0] = calc_load_n(avenrun[0], EXP_1, active, n); > - avenrun[1] = calc_load_n(avenrun[1], EXP_5, active, n); > - avenrun[2] = calc_load_n(avenrun[2], EXP_15, active, n); > + calc_load_update += n * LOAD_FREQ; > + } > > - calc_load_update += n * LOAD_FREQ; > + /* > + * Flip the idle index... > + * > + * Make sure we first write the new time then flip the index, so that > + * calc_load_write_idx() will see the new time when it reads the new > + * index, this avoids a double flip messing things up. > + */ > + smp_wmb(); > + calc_load_idx++; > } > #else > void calc_load_account_idle(struct rq *this_rq) >
I tried to identify the start-line precisely, and made the implemention little more complicated. Using calc_load_update as start-line will cause it not that accurate, but may work, and keep simple. I will test this on my environments, and try to port the next patch on this.
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