| Message ID | 1467781230-12484-4-git-send-email-jgross@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, 6 Jul 2016, Juergen Gross wrote: > Up to now reading the stolen time of a remote cpu was not possible in a > performant way under Xen. This made support of runqueue steal time via > paravirt_steal_rq_enabled impossible. > > With the addition of an appropriate hypervisor interface this is now > possible, so add the support. > > Signed-off-by: Juergen Gross <jgross@suse.com> Reviewed-by: Stefano Stabellini <sstabellini@kernel.org> > V2: removed static variable as requested by Stefano Stabellini > --- > drivers/xen/time.c | 40 +++++++++++++++++++++++----------------- > 1 file changed, 23 insertions(+), 17 deletions(-) > > diff --git a/drivers/xen/time.c b/drivers/xen/time.c > index 2257b66..a7fe35b 100644 > --- a/drivers/xen/time.c > +++ b/drivers/xen/time.c > @@ -47,27 +47,31 @@ static u64 get64(const u64 *p) > return ret; > } > > -/* > - * Runstate accounting > - */ > -void xen_get_runstate_snapshot(struct vcpu_runstate_info *res) > +static void xen_get_runstate_snapshot_cpu(struct vcpu_runstate_info *res, > + unsigned int cpu) > { > u64 state_time; > struct vcpu_runstate_info *state; > > BUG_ON(preemptible()); > > - state = this_cpu_ptr(&xen_runstate); > + state = per_cpu_ptr(&xen_runstate, cpu); > > - /* > - * The runstate info is always updated by the hypervisor on > - * the current CPU, so there's no need to use anything > - * stronger than a compiler barrier when fetching it. > - */ > do { > state_time = get64(&state->state_entry_time); > + rmb(); /* Hypervisor might update data. */ > *res = READ_ONCE(*state); > - } while (get64(&state->state_entry_time) != state_time); > + rmb(); /* Hypervisor might update data. */ > + } while (get64(&state->state_entry_time) != state_time || > + (state_time & XEN_RUNSTATE_UPDATE)); > +} > + > +/* > + * Runstate accounting > + */ > +void xen_get_runstate_snapshot(struct vcpu_runstate_info *res) > +{ > + xen_get_runstate_snapshot_cpu(res, smp_processor_id()); > } > > /* return true when a vcpu could run but has no real cpu to run on */ > @@ -80,8 +84,7 @@ static u64 xen_steal_clock(int cpu) > { > struct vcpu_runstate_info state; > > - BUG_ON(cpu != smp_processor_id()); > - xen_get_runstate_snapshot(&state); > + xen_get_runstate_snapshot_cpu(&state, cpu); > return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline]; > } > > @@ -98,11 +101,14 @@ void xen_setup_runstate_info(int cpu) > > void __init xen_time_setup_guest(void) > { > + bool xen_runstate_remote; > + > + xen_runstate_remote = !HYPERVISOR_vm_assist(VMASST_CMD_enable, > + VMASST_TYPE_runstate_update_flag); > + > pv_time_ops.steal_clock = xen_steal_clock; > > static_key_slow_inc(¶virt_steal_enabled); > - /* > - * We can't set paravirt_steal_rq_enabled as this would require the > - * capability to read another cpu's runstate info. > - */ > + if (xen_runstate_remote) > + static_key_slow_inc(¶virt_steal_rq_enabled); > } > -- > 2.6.6 >
diff --git a/drivers/xen/time.c b/drivers/xen/time.c index 2257b66..a7fe35b 100644 --- a/drivers/xen/time.c +++ b/drivers/xen/time.c @@ -47,27 +47,31 @@ static u64 get64(const u64 *p) return ret; } -/* - * Runstate accounting - */ -void xen_get_runstate_snapshot(struct vcpu_runstate_info *res) +static void xen_get_runstate_snapshot_cpu(struct vcpu_runstate_info *res, + unsigned int cpu) { u64 state_time; struct vcpu_runstate_info *state; BUG_ON(preemptible()); - state = this_cpu_ptr(&xen_runstate); + state = per_cpu_ptr(&xen_runstate, cpu); - /* - * The runstate info is always updated by the hypervisor on - * the current CPU, so there's no need to use anything - * stronger than a compiler barrier when fetching it. - */ do { state_time = get64(&state->state_entry_time); + rmb(); /* Hypervisor might update data. */ *res = READ_ONCE(*state); - } while (get64(&state->state_entry_time) != state_time); + rmb(); /* Hypervisor might update data. */ + } while (get64(&state->state_entry_time) != state_time || + (state_time & XEN_RUNSTATE_UPDATE)); +} + +/* + * Runstate accounting + */ +void xen_get_runstate_snapshot(struct vcpu_runstate_info *res) +{ + xen_get_runstate_snapshot_cpu(res, smp_processor_id()); } /* return true when a vcpu could run but has no real cpu to run on */ @@ -80,8 +84,7 @@ static u64 xen_steal_clock(int cpu) { struct vcpu_runstate_info state; - BUG_ON(cpu != smp_processor_id()); - xen_get_runstate_snapshot(&state); + xen_get_runstate_snapshot_cpu(&state, cpu); return state.time[RUNSTATE_runnable] + state.time[RUNSTATE_offline]; } @@ -98,11 +101,14 @@ void xen_setup_runstate_info(int cpu) void __init xen_time_setup_guest(void) { + bool xen_runstate_remote; + + xen_runstate_remote = !HYPERVISOR_vm_assist(VMASST_CMD_enable, + VMASST_TYPE_runstate_update_flag); + pv_time_ops.steal_clock = xen_steal_clock; static_key_slow_inc(¶virt_steal_enabled); - /* - * We can't set paravirt_steal_rq_enabled as this would require the - * capability to read another cpu's runstate info. - */ + if (xen_runstate_remote) + static_key_slow_inc(¶virt_steal_rq_enabled); }
Up to now reading the stolen time of a remote cpu was not possible in a performant way under Xen. This made support of runqueue steal time via paravirt_steal_rq_enabled impossible. With the addition of an appropriate hypervisor interface this is now possible, so add the support. Signed-off-by: Juergen Gross <jgross@suse.com> --- V2: removed static variable as requested by Stefano Stabellini --- drivers/xen/time.c | 40 +++++++++++++++++++++++----------------- 1 file changed, 23 insertions(+), 17 deletions(-)