On 06/15/2015 11:20 AM, Marc Zyngier wrote: > On 15/06/15 19:04, Mario Smarduch wrote: >> On 06/15/2015 03:00 AM, Marc Zyngier wrote: >>> Hi Mario, >>> >>> I was working on a more ambitious patch series, >>> but we probably ought to >>> start small, and this looks fairly sensible to me. >> >> Hi Marc, >> thanks for reviewing, I was thinking to post this >> first and next iteration on guest access switch >> back to host registers only upon return to user space or >> vCPU context switch. This should save more cycles for >> various exits. >> >> Were you thinking along the same lines or something >> altogether different? > > That's mostly what I had in mind. Basically staying away from touching > the FP registers until vcpu_put(). I had it mostly working, but > experienced some interesting corruption cases, specially when using > 32bit guests. > >> >>> >>> A few minor comments below. >>> >>> On 13/06/15 23:20, Mario Smarduch wrote: >>>> Currently VFP/SIMD registers are always saved and restored >>>> on Guest entry and exit. >>>> >>>> This patch only saves and restores VFP/SIMD registers on >>>> Guest access. To do this cptr_el2 VFP/SIMD trap is set >>>> on Guest entry and later checked on exit. This follows >>>> the ARMv7 VFPv3 implementation. Running an informal test >>>> there are high number of exits that don't access VFP/SIMD >>>> registers. >>> >>> It would be good to add some numbers here. How often do we exit without >>> having touched the FPSIMD regs? For which workload? >> >> Lmbench is what I typically use, with ssh server, i.e., cause page >> faults and interrupts - usually registers are not touched. >> I'll run the tests again and define usually. >> >> Any other loads you had in mind? > > Not really (apart from running hackbench, of course...;-). I'd just like > to see the numbers in the commit message, so that we can document the > improvement (and maybe track regressions). Ok I understand. > > [...] > >>> >>>> skip_debug_state x3, 1f >>>> // Clear the dirty flag for the next run, as all the state has >>>> // already been saved. Note that we nuke the whole 64bit word. >>>> @@ -1166,6 +1211,10 @@ el1_sync: // Guest trapped into EL2 >>>> mrs x1, esr_el2 >>>> lsr x2, x1, #ESR_ELx_EC_SHIFT >>>> >>>> + /* Guest accessed VFP/SIMD registers, save host, restore Guest */ >>>> + cmp x2, #ESR_ELx_EC_FP_ASIMD >>>> + b.eq switch_to_guest_vfp >>>> + >>> >>> I'd prefer you moved that hunk to el1_trap, where we handle all the >>> traps coming from the guest. >> >> I'm thinking would it make sense to update the armv7 side as >> well. When reading both exit handlers the flow mirrors >> each other. > > The 32bit code is starting to show its age, and could probably do with a > refactor. If you have some cycles to spare, that'd be quite interesting. Yep, will do, ARMv7 is still very relevant. > > Thanks, > > M. > -- 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
