| Message ID | 1470378840-15206-1-git-send-email-leo.yan@linaro.org |
|---|---|
| State | New |
| Headers | show |
Hi Leo, On 5 August 2016 at 08:34, Leo Yan <leo.yan@linaro.org> wrote: > > In current code, decay_load() will consider to set load value to zero > after passing 32*64 ms. So this means max_load * (0.5^64) ~= 0. > > Kernel can support maximum number of processes and threads to 2^29 and > set task with highest priority with nice=-20 (weight = 88761). So in > worst case, one CPU may have maximum load value is: > > max_load = 2^29 * 88761 < 2^46 > > In theory after pass 46 periods we can ensure load value will be decayed > to zero. So this patch is to change maximum periods from 64 to 48. > > Signed-off-by: Leo Yan <leo.yan@linaro.org> > --- > kernel/sched/fair.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index e342159..55cb134 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -2622,7 +2622,7 @@ static __always_inline u64 decay_load(u64 val, u64 n) > > if (!n) > return val; > - else if (unlikely(n > LOAD_AVG_PERIOD * 63)) > + else if (unlikely(n > LOAD_AVG_PERIOD * 47)) In the equation above, you use 46 then you mentioned : "change maximum periods from 64 to 48." and finally you use 47. > return 0; > > /* after bounds checking we can collapse to 32-bit */ > -- > 1.9.1 >
Hi Vincent, Thanks for review. On Fri, Aug 05, 2016 at 09:56:46AM +0200, Vincent Guittot wrote: > Hi Leo, > > On 5 August 2016 at 08:34, Leo Yan <leo.yan@linaro.org> wrote: > > > > In current code, decay_load() will consider to set load value to zero > > after passing 32*64 ms. So this means max_load * (0.5^64) ~= 0. > > > > Kernel can support maximum number of processes and threads to 2^29 and > > set task with highest priority with nice=-20 (weight = 88761). So in > > worst case, one CPU may have maximum load value is: > > > > max_load = 2^29 * 88761 < 2^46 > > > > In theory after pass 46 periods we can ensure load value will be decayed > > to zero. So this patch is to change maximum periods from 64 to 48. > > > > Signed-off-by: Leo Yan <leo.yan@linaro.org> > > --- > > kernel/sched/fair.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index e342159..55cb134 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -2622,7 +2622,7 @@ static __always_inline u64 decay_load(u64 val, u64 n) > > > > if (!n) > > return val; > > - else if (unlikely(n > LOAD_AVG_PERIOD * 63)) > > + else if (unlikely(n > LOAD_AVG_PERIOD * 47)) > > In the equation above, you use 46 then you mentioned : "change maximum > periods from 64 to 48." and finally you use 47. Sorry introduce confusion. I want to align to 16 so choose maximum periods to 48, and due to condition is (n > LOAD_AVG_PERIOD * 47) so it equeals to (n >= LOAD_AVG_PERIOD * 48). Precisely I think the code should be: else if (unlikely(n >= LOAD_AVG_PERIOD * 46)) Do you think this is okay? > > return 0; > > > > /* after bounds checking we can collapse to 32-bit */ > > -- > > 1.9.1 > >
On 5 August 2016 at 10:17, Leo Yan <leo.yan@linaro.org> wrote: > Hi Vincent, > > Thanks for review. > > On Fri, Aug 05, 2016 at 09:56:46AM +0200, Vincent Guittot wrote: >> Hi Leo, >> >> On 5 August 2016 at 08:34, Leo Yan <leo.yan@linaro.org> wrote: >> > >> > In current code, decay_load() will consider to set load value to zero >> > after passing 32*64 ms. So this means max_load * (0.5^64) ~= 0. >> > >> > Kernel can support maximum number of processes and threads to 2^29 and >> > set task with highest priority with nice=-20 (weight = 88761). So in >> > worst case, one CPU may have maximum load value is: >> > >> > max_load = 2^29 * 88761 < 2^46 >> > >> > In theory after pass 46 periods we can ensure load value will be decayed >> > to zero. So this patch is to change maximum periods from 64 to 48. >> > >> > Signed-off-by: Leo Yan <leo.yan@linaro.org> >> > --- >> > kernel/sched/fair.c | 2 +- >> > 1 file changed, 1 insertion(+), 1 deletion(-) >> > >> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> > index e342159..55cb134 100644 >> > --- a/kernel/sched/fair.c >> > +++ b/kernel/sched/fair.c >> > @@ -2622,7 +2622,7 @@ static __always_inline u64 decay_load(u64 val, u64 n) >> > >> > if (!n) >> > return val; >> > - else if (unlikely(n > LOAD_AVG_PERIOD * 63)) >> > + else if (unlikely(n > LOAD_AVG_PERIOD * 47)) >> >> In the equation above, you use 46 then you mentioned : "change maximum >> periods from 64 to 48." and finally you use 47. > > Sorry introduce confusion. I want to align to 16 so choose maximum > periods to 48, and due to condition is (n > LOAD_AVG_PERIOD * 47) so > it equeals to (n >= LOAD_AVG_PERIOD * 48). > > Precisely I think the code should be: > else if (unlikely(n >= LOAD_AVG_PERIOD * 46)) > > Do you think this is okay? yes, this looks okay > >> > return 0; >> > >> > /* after bounds checking we can collapse to 32-bit */ >> > -- >> > 1.9.1 >> >
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index e342159..55cb134 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2622,7 +2622,7 @@ static __always_inline u64 decay_load(u64 val, u64 n) if (!n) return val; - else if (unlikely(n > LOAD_AVG_PERIOD * 63)) + else if (unlikely(n > LOAD_AVG_PERIOD * 47)) return 0; /* after bounds checking we can collapse to 32-bit */
In current code, decay_load() will consider to set load value to zero after passing 32*64 ms. So this means max_load * (0.5^64) ~= 0. Kernel can support maximum number of processes and threads to 2^29 and set task with highest priority with nice=-20 (weight = 88761). So in worst case, one CPU may have maximum load value is: max_load = 2^29 * 88761 < 2^46 In theory after pass 46 periods we can ensure load value will be decayed to zero. So this patch is to change maximum periods from 64 to 48. Signed-off-by: Leo Yan <leo.yan@linaro.org> --- kernel/sched/fair.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) -- 1.9.1