"J.A. Magallón" <[email protected]> writes: > 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: > > register int tmp_a = *ina; > register int tmp_b = *inb; > > for (int i=0; i<10; i++) > { > a[i] = tmp_a; > b[i] = tmp_b; > } > > because nor 'ina' nor 'inb' change under what the compiler sees inside > the loop. 'volatile' prevents the compiler of do a high level cache of > *ina or *inb. Actually the compiler may not do any of these transformations because *ina or *inb may alias any of a[i] or b[i]. Andreas. -- Andreas Schwab, SuSE Labs, [email protected] SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany PGP key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5 "And now for something completely different." - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
- References:
- Re: [patch] uninline init_waitqueue_*() functions
- From: Ingo Molnar <[email protected]>
- Re: [patch] uninline init_waitqueue_*() functions
- From: Andrew Morton <[email protected]>
- Re: [patch] uninline init_waitqueue_*() functions
- From: Ingo Molnar <[email protected]>
- Re: [patch] uninline init_waitqueue_*() functions
- From: Andrew Morton <[email protected]>
- Re: [patch] uninline init_waitqueue_*() functions
- From: Linus Torvalds <[email protected]>
- Re: [patch] uninline init_waitqueue_*() functions
- From: Ingo Molnar <[email protected]>
- Re: [patch] uninline init_waitqueue_*() functions
- From: Linus Torvalds <[email protected]>
- Re: [patch] uninline init_waitqueue_*() functions
- From: Ingo Molnar <[email protected]>
- Re: [patch] uninline init_waitqueue_*() functions
- From: Linus Torvalds <[email protected]>
- Re: [patch] uninline init_waitqueue_*() functions
- From: Linus Torvalds <[email protected]>
- [patch] spinlocks: remove 'volatile'
- From: Ingo Molnar <[email protected]>
- Re: [patch] spinlocks: remove 'volatile'
- From: "linux-os \(Dick Johnson\)" <[email protected]>
- Re: [patch] spinlocks: remove 'volatile'
- From: Arjan van de Ven <[email protected]>
- Re: [patch] spinlocks: remove 'volatile'
- From: "linux-os \(Dick Johnson\)" <[email protected]>
- Re: [patch] spinlocks: remove 'volatile'
- From: Arjan van de Ven <[email protected]>
- Re: [patch] spinlocks: remove 'volatile'
- From: "J.A. Magallón" <[email protected]>
- Re: [patch] uninline init_waitqueue_*() functions
- Prev by Date: [git pull] jfs update
- Next by Date: Re: How to reset pci device
- Previous by thread: Re: [patch] spinlocks: remove 'volatile'
- Next by thread: Re: [patch] spinlocks: remove 'volatile'
- Index(es):
 |