On Sun, Dec 8, 2013 at 2:54 AM, Xin Tong <trent.t...@gmail.com> wrote: > > > > On Thu, Nov 28, 2013 at 8:12 AM, Lluís Vilanova <vilan...@ac.upc.edu> wrote: >> >> Xin Tong writes: >> >> > Hi LIuis >> > we can probably generate vector intrinsics using the tcg, e.g. add >> > support to >> > tcg to emit vector instructions directly in code cache >> >> There was some discussion long ago about adding vector instructions to >> TCG, but >> I don't remember what was the conclusion. >> >> Also remember that using vector instructions will "emulate" a >> low-associativity >> TLB; don't know how much better than a 1-way TLB will that be, though. >> >> >> > why would a larger TLB make some operations slower, the TLB is a >> > direct-mapped >> > hash and lookup should be O(1) there. In the cputlb, the CPU_TLB_SIZE is >> > always >> > used to index into the TLB, i.e. (X & (CPU_TLB_SIZE -1)). >> >> It would make TLB invalidations slower (e.g., see 'tlb_flush' in >> "cputlb.c"). And right now QEMU performs full TLB invalidations more >> frequently >> than the equivalent HW needs to, although I suppose that should be >> quantified >> too.
I see QEMU executed ~1M instructions per context switch for qemu-system-x86_64. Is this because of the fact that the periodical time interval interrupt is delivered in real time while QEMU is significantly slower than real hw ? Xin >> > you are right LIuis. QEMU does context switch quite more often that real hw, > this is probably primarily due to the fact that QEMU is magnitude slower > than real hw. I am wondering where timer is emulated in QEMU system-x86_64. > I imagine the guest OS must program the timers to do interrupt for context > switches. > > Another question, what happens when a vcpu is stuck in an infinite loop ? > QEMU must need an timer interrupt somewhere as well ? > > Is my understanding correct ? > > Xin >> >> >> Lluis >> >> -- >> "And it's much the same thing with knowledge, for whenever you learn >> something new, the whole world becomes that much richer." >> -- The Princess of Pure Reason, as told by Norton Juster in The Phantom >> Tollbooth > >
