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). [...] >> >>> 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. Thanks, M. -- Jazz is not dead. It just smells funny... -- 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
