Messages in this thread | | | Date | Mon, 22 Oct 2012 15:08:10 +0200 | From | Gleb Natapov <> | Subject | Re: [PATCH] KVM: x86: fix vcpu->mmio_fragments overflow |
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On Mon, Oct 22, 2012 at 03:05:58PM +0200, Jan Kiszka wrote: > On 2012-10-22 14:58, Avi Kivity wrote: > > On 10/22/2012 02:55 PM, Jan Kiszka wrote: > >>> Since the userspace change is needed the idea is dead, but if we could > >>> implement it I do not see how it can hurt the latency if it would be the > >>> only mechanism to use coalesced mmio buffer. Checking that the ring buffer > >>> is empty is cheap and if it is not empty it means that kernel just saved > >>> you a lot of 8 bytes exists so even after iterating over all the entries there > >>> you still saved a lot of time. > >> > >> When taking an exit for A, I'm not interesting in flushing stuff for B > >> unless I have a dependency. Thus, buffers would have to be per device > >> before extending their use. > > > > Any mmio exit has to flush everything. For example a DMA caused by an > > e1000 write has to see any writes to the framebuffer, in case the guest > > is transmitting its framebuffer to the outside world. > > We already flush when that crazy guest actually accesses the region, no > need to do this unconditionally. > What if framebuffer is accessed from inside the kernel? Is this case handled?
-- Gleb.
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