Messages in this thread | | | Date | Tue, 26 Jan 2010 19:07:48 +1100 | From | Anton Blanchard <> | Subject | Re: [PATCH] sched: cpuacct: Use bigger percpu counter batch values for stats counters |
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Hi Andrew,
> > I guess a lot of the changelog and comments are in the email history, > > Not a very useful location for it!
Good point, I'll work on a useful comment.
> > Why does it look quite wrong to you? > > Because it computes the correct value and then if it's larger than > INT_MAX, it inexplicably assigns INT_MAX to it, giving a wrong result! > > Does that code actually work, btw? percpu_counter_batch has type `int' > and cputime_one_jiffy has type `int' so their product has type `int'. > So by the time min_t performs its comparison, the upper 32 bits of the > product are already lost.
On ppc64, s390 and ia64 cputime_one_jiffy is 64bit and I want to prevent us creating too large a batch value:
void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch)
If we pass in something bigger than INT_MAX we could end up with 0 after truncation which will turn the percpu counter into a single spinlock global counter.
Anton
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