Messages in this thread | | | Date | Thu, 13 Sep 2018 21:14:22 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v4 02/16] sched/core: uclamp: map TASK's clamp values into CPU's clamp groups |
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On Wed, Sep 12, 2018 at 06:52:02PM +0100, Patrick Bellasi wrote: > On 12-Sep 19:42, Peter Zijlstra wrote: > > On Wed, Sep 12, 2018 at 06:35:15PM +0100, Patrick Bellasi wrote: > > > On 12-Sep 18:12, Peter Zijlstra wrote: > > > > > > No idea; but if you want to go all fancy you can replace he whole > > > > uclamp_map thing with something like: > > > > > > > > struct uclamp_map { > > > > union { > > > > struct { > > > > unsigned long v : 10; > > > > unsigned long c : BITS_PER_LONG - 10; > > > > }; > > > > atomic_long_t s; > > > > }; > > > > }; > > > > > > That sounds really cool and scary at the same time :) > > > > > > The v:10 requires that we never set SCHED_CAPACITY_SCALE>1024 > > > or that we use it to track a percentage value (i.e. [0..100]). > > > > Or we pick 11 bits, it seems unlikely that capacity be larger than 2k. > > Just remembered a past experience where we had unaligned access traps > on some machine because... don't you see any potentially issue on > using bitfleds like you suggest above ? > > I'm thinking to: > > commit 317d359df95d ("sched/core: Force proper alignment of 'struct util_est'")
There should not be (and I'm still confused by that particular commit you reference). If we access everything through the uclamp_map::s, and only use the bitfields to interpret the results, it all 'works'.
The tricky thing we did earlier was trying to use u64 accesses for 2 u32 variables. And somehow ia64 didn't get the alignment right.
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