On 13/12/2017 20:19, Alexander Graf wrote: > > > On 02.02.17 06:14, David Gibson wrote: >> From: Laurent Vivier <lviv...@redhat.com> >> >> This is a port to ppc of the i386 commit: >> 00f4d64 kvmclock: clock should count only if vm is running >> >> We remove timebase_post_load function, and use the VM state >> change handler to save and restore the guest_timebase (on stop >> and continue). >> >> We keep timebase_pre_save to reduce the clock difference on >> migration like in: >> 6053a86 kvmclock: reduce kvmclock difference on migration >> >> Time base offset has originally been introduced by commit >> 98a8b52 spapr: Add support for time base offset migration >> >> So while VM is paused, the time is stopped. This allows to have >> the same result with date (based on Time Base Register) and >> hwclock (based on "get-time-of-day" RTAS call). >> >> Moreover in TCG mode, the Time Base is always paused, so this >> patch also adjust the behavior between TCG and KVM. >> >> VM state field "time_of_the_day_ns" is now useless but we keep >> it to be able to migrate to older version of the machine. >> >> As vmstate_ppc_timebase structure (with timebase_pre_save() and >> timebase_post_load() functions) was only used by vmstate_spapr, >> we register the VM state change handler only in ppc_spapr_init(). >> >> Signed-off-by: Laurent Vivier <lviv...@redhat.com> >> Signed-off-by: David Gibson <da...@gibson.dropbear.id.au> > > Just a small heads-up: I've been debugging an OpenQA regression lately > where our automated testing regressed with QEMU 2.9. With stock 2.9.1, I > get a failure rate of "weird" effects (probably TB divergence between > vcpus) of ~30%. With this patch reverted it's back to 0%. > > I *think* something here causes the TB offset of multiple threads (I'm > running -smp 2,threads=2) to diverge. > > I'll keep debugging things tomorrow, but I'll be happy to see anyone > else beat me to analyze what is going wrong ;).
Don't know if it can be related, but for migration we need: http://patchwork.ozlabs.org/patch/840170/ diff --git a/target/ppc/translate_init.c b/target/ppc/translate_init.c index b9c49c22f2..4e11e6f489 100644 --- a/target/ppc/translate_init.c +++ b/target/ppc/translate_init.c @@ -8081,10 +8081,10 @@ static void gen_spr_power8_ebb(CPUPPCState *env) /* Virtual Time Base */ static void gen_spr_vtb(CPUPPCState *env) { - spr_register(env, SPR_VTB, "VTB", + spr_register_kvm(env, SPR_VTB, "VTB", SPR_NOACCESS, SPR_NOACCESS, &spr_read_tbl, SPR_NOACCESS, - 0x00000000); + KVM_REG_PPC_VTB, 0x00000000); } static void gen_spr_power8_fscr(CPUPPCState *env) Thanks, Laurent
