Messages in this thread | | | Subject | Re: [patch] spinlocks: remove 'volatile' | From | Arjan van de Ven <> | Date | Thu, 06 Jul 2006 15:43:14 +0200 |
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> > I did not talk about memory barriers. In fact, barrier() is NOT a memory > > barrier. It's a compiler optimization barrier! > > > > // Read 10 samples from 2 A/D converters. > > int* ina; > int a[10]; > int* inb; > int b[10]; > > for (int i=0; i<10; i++) > { > a[i] = *ina; > barrier(); > b[i] = *inb; > } > > The barrier prevents the compiler of translating this to: > > for (int i=0; i<10; i++) > { > b[i] = *inb; > a[i] = *ina; > } > > or even to: > > for (int i=0; i<10; i++) > a[i] = *ina; > for (int i=0; i<10; i++) > b[i] = *inb; > > but does not prevent it to do this:
yes it does. It's a full optimization barrier; the compiler assumes all register and memory content has changed from before the barrier(), and it will start "fresh".
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