On Thu, Aug 27, 2009 at 04:24:58PM +0300, Avi Kivity wrote: > On 08/27/2009 03:45 PM, Marcelo Tosatti wrote: >>> Why not bool guest_mode? Saves two atomics per exit. >>> >> It must be atomic since GUEST_MODE / VCPU_KICKED bits are manipulated by >> multiple CPU's. >> > > bools are atomic. OK. - VCPU_KICKED requires test_and_set. GUEST_MODE/VCPU_KICKED accesses must not be reordered. (OK, could have GUEST_MODE in a bool even so, but its easier to read by keeping them together, at least to me). - Its easier to cacheline align with longs rather than bools? - From testing it seems the LOCK prefix is not heavy, as long as its cpu local (probably due to 7.1.4 Effects of a LOCK Operation on Internal Processor Caches?). BTW, 7.1.2.2 Software Controlled Bus Locking Software should access semaphores (shared memory used for signalling between multiple processors) using identical addresses and operand lengths. For example, if one processor accesses a semaphore using a word access, other processors should not access the semaphore using a byte access. The bit operations use 32-bit access, but the vcpu->requests check in vcpu_enter_guest uses 64-bit access. Is that safe? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
