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KVM: s390: handle access registers in the run ioctl not in vcpu_put/load 

Right now we save the host access registers in kvm_arch_vcpu_load
and load them in kvm_arch_vcpu_put. Vice versa for the guest access
registers. On schedule this means, that we load/save access registers
multiple times.

e.g. VCPU_RUN with just one reschedule and then return does

[from user space via VCPU_RUN]
- save the host registers in kvm_arch_vcpu_load (via ioctl)
- load the guest registers in kvm_arch_vcpu_load (via ioctl)
- do guest stuff
- decide to schedule/sleep
- save the guest registers in kvm_arch_vcpu_put (via sched)
- load the host registers in kvm_arch_vcpu_put (via sched)
- save the host registers in switch_to (via sched)
- schedule
- return
- load the host registers in switch_to (via sched)
- save the host registers in kvm_arch_vcpu_load (via sched)
- load the guest registers in kvm_arch_vcpu_load (via sched)
- do guest stuff
- decide to go to userspace
- save the guest registers in kvm_arch_vcpu_put (via ioctl)
- load the host registers in kvm_arch_vcpu_put (via ioctl)
[back to user space]

As the kernel does not use access registers, we can avoid
this reloading and simply piggy back on switch_to (let it save
the guest values instead of host values in thread.acrs) by
moving the host/guest switch into the VCPU_RUN ioctl function.
We now do

[from user space via VCPU_RUN]
- save the host registers in kvm_arch_vcpu_ioctl_run
- load the guest registers in kvm_arch_vcpu_ioctl_run
- do guest stuff
- decide to schedule/sleep
- save the guest registers in switch_to
- schedule
- return
- load the guest registers in switch_to (via sched)
- do guest stuff
- decide to go to userspace
- save the guest registers in kvm_arch_vcpu_ioctl_run
- load the host registers in kvm_arch_vcpu_ioctl_run

This seems to save about 10% of the vcpu_put/load functions
according to perf.

As vcpu_load no longer switches the acrs, We can also loading
the acrs in kvm_arch_vcpu_ioctl_set_sregs.

Suggested-by: Fan Zhang <zhangfan@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
This commit is contained in:
Christian Borntraeger 2016-11-10 14:22:02 +01:00
parent 813ae37e6a
commit 31d8b8d41a
2 changed files with 6 additions and 8 deletions
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2
arch/s390/kvm/interrupt.c
View File

@ -415,7 +415,7 @@ static int __write_machine_check(struct kvm_vcpu *vcpu,
int rc;
mci.val = mchk->mcic;
/* take care of lazy register loading via vcpu load/put */
/* take care of lazy register loading */
save_fpu_regs();
save_access_regs(vcpu->run->s.regs.acrs);

12
arch/s390/kvm/kvm-s390.c
View File

@ -1826,8 +1826,6 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
/* User space provided an invalid FPC, let's clear it */
current->thread.fpu.fpc = 0;
save_access_regs(vcpu->arch.host_acrs);
restore_access_regs(vcpu->run->s.regs.acrs);
gmap_enable(vcpu->arch.enabled_gmap);
atomic_or(CPUSTAT_RUNNING, &vcpu->arch.sie_block->cpuflags);
if (vcpu->arch.cputm_enabled && !is_vcpu_idle(vcpu))
@ -1851,9 +1849,6 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
/* Restore host register state */
current->thread.fpu.fpc = vcpu->arch.host_fpregs.fpc;
current->thread.fpu.regs = vcpu->arch.host_fpregs.regs;
save_access_regs(vcpu->run->s.regs.acrs);
restore_access_regs(vcpu->arch.host_acrs);
}
static void kvm_s390_vcpu_initial_reset(struct kvm_vcpu *vcpu)
@ -2243,7 +2238,6 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
{
memcpy(&vcpu->run->s.regs.acrs, &sregs->acrs, sizeof(sregs->acrs));
memcpy(&vcpu->arch.sie_block->gcr, &sregs->crs, sizeof(sregs->crs));
restore_access_regs(vcpu->run->s.regs.acrs);
return 0;
}
@ -2740,6 +2734,8 @@ static void sync_regs(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
if (riccb->valid)
vcpu->arch.sie_block->ecb3 |= 0x01;
}
save_access_regs(vcpu->arch.host_acrs);
restore_access_regs(vcpu->run->s.regs.acrs);
kvm_run->kvm_dirty_regs = 0;
}
@ -2758,6 +2754,8 @@ static void store_regs(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
kvm_run->s.regs.pft = vcpu->arch.pfault_token;
kvm_run->s.regs.pfs = vcpu->arch.pfault_select;
kvm_run->s.regs.pfc = vcpu->arch.pfault_compare;
save_access_regs(vcpu->run->s.regs.acrs);
restore_access_regs(vcpu->arch.host_acrs);
}
int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
@ -2874,7 +2872,7 @@ int kvm_s390_vcpu_store_status(struct kvm_vcpu *vcpu, unsigned long addr)
{
/*
* The guest FPRS and ACRS are in the host FPRS/ACRS due to the lazy
* copying in vcpu load/put. Lets update our copies before we save
* switch in the run ioctl. Let's update our copies before we save
* it into the save area
*/
save_fpu_regs();