On Fri, Mar 10, 2017 at 03:37:16PM +0530, Bharata B Rao wrote:
> On Fri, Mar 10, 2017 at 6:43 AM, David Gibson <da...@gibson.dropbear.id.au>
> wrote:
>
> > This patch implements hypercalls allowing a PAPR guest to resize its own
> > hash page table. This will eventually allow for more flexible memory
> > hotplug.
> >
> > The implementation is partially asynchronous, handled in a special thread
> > running the hpt_prepare_thread() function. The state of a pending resize
> > is stored in SPAPR_MACHINE->pending_hpt.
> >
> > The H_RESIZE_HPT_PREPARE hypercall will kick off creation of a new HPT, or,
> > if one is already in progress, monitor it for completion. If there is an
> > existing HPT resize in progress that doesn't match the size specified in
> > the call, it will cancel it, replacing it with a new one matching the
> > given size.
> >
> > The H_RESIZE_HPT_COMMIT completes transition to a resized HPT, and can only
> > be called successfully once H_RESIZE_HPT_PREPARE has successfully
> > completed initialization of a new HPT. The guest must ensure that there
> > are no concurrent accesses to the existing HPT while this is called (this
> > effectively means stop_machine() for Linux guests).
> >
> > For now H_RESIZE_HPT_COMMIT goes through the whole old HPT, rehashing each
> > HPTE into the new HPT. This can have quite high latency, but it seems to
> > be of the order of typical migration downtime latencies for HPTs of size
> > up to ~2GiB (which would be used in a 256GiB guest).
> >
> > In future we probably want to move more of the rehashing to the "prepare"
> > phase, by having H_ENTER and other hcalls update both current and
> > pending HPTs. That's a project for another day, but should be possible
> > without any changes to the guest interface.
> >
> > Signed-off-by: David Gibson <da...@gibson.dropbear.id.au>
> > ---
> > hw/ppc/spapr.c | 4 +-
> > hw/ppc/spapr_hcall.c | 338 ++++++++++++++++++++++++++++++
> > +++++++++++++++++-
> > include/hw/ppc/spapr.h | 6 +
> > target/ppc/mmu-hash64.h | 4 +
> > 4 files changed, 346 insertions(+), 6 deletions(-)
> >
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index 06b436d..bf6ba64 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -94,8 +94,6 @@
> >
> > #define PHANDLE_XICP 0x00001111
> >
> > -#define HTAB_SIZE(spapr) (1ULL << ((spapr)->htab_shift))
> > -
> > static int try_create_xics(sPAPRMachineState *spapr, const char
> > *type_ics,
> > const char *type_icp, int nr_servers,
> > int nr_irqs, Error **errp)
> > @@ -1169,7 +1167,7 @@ static void spapr_store_hpte(PPCVirtualHypervisor
> > *vhyp, hwaddr ptex,
> > }
> > }
> >
> > -static int spapr_hpt_shift_for_ramsize(uint64_t ramsize)
> > +int spapr_hpt_shift_for_ramsize(uint64_t ramsize)
> > {
> > int shift;
> >
> > diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> > index 9f88960..4c0b0fb 100644
> > --- a/hw/ppc/spapr_hcall.c
> > +++ b/hw/ppc/spapr_hcall.c
> > @@ -3,6 +3,7 @@
> > #include "sysemu/hw_accel.h"
> > #include "sysemu/sysemu.h"
> > #include "qemu/log.h"
> > +#include "qemu/error-report.h"
> > #include "cpu.h"
> > #include "exec/exec-all.h"
> > #include "helper_regs.h"
> > @@ -352,20 +353,316 @@ static target_ulong h_read(PowerPCCPU *cpu,
> > sPAPRMachineState *spapr,
> > return H_SUCCESS;
> > }
> >
> > +struct sPAPRPendingHPT {
> > + /* These fields are read-only after initialization */
> > + int shift;
> > + QemuThread thread;
> > +
> > + /* These fields are protected by the BQL */
> > + bool complete;
> > +
> > + /* These fields are private to the preparation thread if
> > + * !complete, otherwise protected by the BQL */
> > + int ret;
> > + void *hpt;
> > +};
> > +
> > +static void free_pending_hpt(sPAPRPendingHPT *pending)
> > +{
> > + if (pending->hpt) {
> > + qemu_vfree(pending->hpt);
> > + }
> > +
> > + g_free(pending);
> > +}
> > +
> > +static void *hpt_prepare_thread(void *opaque)
> > +{
> > + sPAPRPendingHPT *pending = opaque;
> > + size_t size = 1ULL << pending->shift;
> > +
> > + pending->hpt = qemu_memalign(size, size);
> > + if (pending->hpt) {
> > + memset(pending->hpt, 0, size);
> > + pending->ret = H_SUCCESS;
> > + } else {
> > + pending->ret = H_NO_MEM;
> > + }
> > +
> > + qemu_mutex_lock_iothread();
> > +
> > + if (SPAPR_MACHINE(qdev_get_machine())->pending_hpt == pending) {
> > + /* Ready to go */
> > + pending->complete = true;
> > + } else {
> > + /* We've been cancelled, clean ourselves up */
> > + free_pending_hpt(pending);
> > + }
> > +
> > + qemu_mutex_unlock_iothread();
> > + return NULL;
> > +}
> > +
> > +/* Must be called with BQL held */
> > +static void cancel_hpt_prepare(sPAPRMachineState *spapr)
> > +{
> > + sPAPRPendingHPT *pending = spapr->pending_hpt;
> > +
> > + /* Let the thread know it's cancelled */
> > + spapr->pending_hpt = NULL;
> > +
> > + if (!pending) {
> > + /* Nothing to do */
> > + return;
> > + }
> > +
> > + if (!pending->complete) {
> > + /* thread will clean itself up */
> > + return;
> > + }
> > +
> > + free_pending_hpt(pending);
> > +}
> > +
> > +static int build_dimm_list(Object *obj, void *opaque)
> > +{
> > + GSList **list = opaque;
> > +
> > + if (object_dynamic_cast(obj, TYPE_PC_DIMM)) {
> > + DeviceState *dev = DEVICE(obj);
> > + if (dev->realized) { /* only realized DIMMs matter */
> > + *list = g_slist_prepend(*list, dev);
> > + }
> > + }
> > +
> > + object_child_foreach(obj, build_dimm_list, opaque);
> > + return 0;
> > +}
> > +
> > +static ram_addr_t get_current_ram_size(void)
> > +{
> > + GSList *list = NULL, *item;
> > + ram_addr_t size = ram_size;
> > +
> > + build_dimm_list(qdev_get_machine(), &list);
> > + for (item = list; item; item = g_slist_next(item)) {
> > + Object *obj = OBJECT(item->data);
> > + if (!strcmp(object_get_typename(obj), TYPE_PC_DIMM)) {
> > + size += object_property_get_int(obj, PC_DIMM_SIZE_PROP,
> > + &error_abort);
> > + }
> > + }
> >
>
> You could use the existing API pc_existing_dimms_capacity() for the
> above.
Good idea, thanks.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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