On Mon, Dec 21, 2020 at 01:08:53PM +0100, Greg Kurz wrote:
> Hi Shiva,
>
> On Mon, 30 Nov 2020 09:16:39 -0600
> Shivaprasad G Bhat <sbhat@xxxxxxxxxxxxx> wrote:
>
> > The patch adds support for async hcalls at the DRC level for the
> > spapr devices. To be used by spapr-scm devices in the patch/es to follow.
> >
> > Signed-off-by: Shivaprasad G Bhat <sbhat@xxxxxxxxxxxxx>
> > ---
>
> The overall idea looks good but I think you should consider using
> a thread pool to implement it. See below.
I am not convinced, however. Specifically, attaching this to the DRC
doesn't make sense to me. We're adding exactly one DRC related async
hcall, and I can't really see much call for another one. We could
have other async hcalls - indeed we already have one for HPT resizing
- but attaching this to DRCs doesn't help for those.
>
> > hw/ppc/spapr_drc.c | 149 ++++++++++++++++++++++++++++++++++++++++++++
> > include/hw/ppc/spapr_drc.h | 25 +++++++
> > 2 files changed, 174 insertions(+)
> >
> > diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c
> > index 77718cde1f..4ecd04f686 100644
> > --- a/hw/ppc/spapr_drc.c
> > +++ b/hw/ppc/spapr_drc.c
> > @@ -15,6 +15,7 @@
> > #include "qapi/qmp/qnull.h"
> > #include "cpu.h"
> > #include "qemu/cutils.h"
> > +#include "qemu/guest-random.h"
> > #include "hw/ppc/spapr_drc.h"
> > #include "qom/object.h"
> > #include "migration/vmstate.h"
> > @@ -421,6 +422,148 @@ void spapr_drc_detach(SpaprDrc *drc)
> > spapr_drc_release(drc);
> > }
> >
> > +
> > +/*
> > + * @drc : device DRC targetting which the async hcalls to be made.
> > + *
> > + * All subsequent requests to run/query the status should use the
> > + * unique token returned here.
> > + */
> > +uint64_t spapr_drc_get_new_async_hcall_token(SpaprDrc *drc)
> > +{
> > + Error *err = NULL;
> > + uint64_t token;
> > + SpaprDrcDeviceAsyncHCallState *tmp, *next, *state;
> > +
> > + state = g_malloc0(sizeof(*state));
> > + state->pending = true;
> > +
> > + qemu_mutex_lock(&drc->async_hcall_states_lock);
> > +retry:
> > + if (qemu_guest_getrandom(&token, sizeof(token), &err) < 0) {
> > + error_report_err(err);
> > + g_free(state);
> > + qemu_mutex_unlock(&drc->async_hcall_states_lock);
> > + return 0;
> > + }
> > +
> > + if (!token) /* Token should be non-zero */
> > + goto retry;
> > +
> > + if (!QLIST_EMPTY(&drc->async_hcall_states)) {
> > + QLIST_FOREACH_SAFE(tmp, &drc->async_hcall_states, node, next) {
> > + if (tmp->continue_token == token) {
> > + /* If the token already in use, get a new one */
> > + goto retry;
> > + }
> > + }
> > + }
> > +
> > + state->continue_token = token;
> > + QLIST_INSERT_HEAD(&drc->async_hcall_states, state, node);
> > +
> > + qemu_mutex_unlock(&drc->async_hcall_states_lock);
> > +
> > + return state->continue_token;
> > +}
> > +
> > +static void *spapr_drc_async_hcall_runner(void *opaque)
> > +{
> > + int response = -1;
> > + SpaprDrcDeviceAsyncHCallState *state = opaque;
> > +
> > + /*
> > + * state is freed only after this thread finishes(after pthread_join()),
> > + * don't worry about it becoming NULL.
> > + */
> > +
> > + response = state->func(state->data);
> > +
> > + state->hcall_ret = response;
> > + state->pending = 0;
> > +
> > + return NULL;
> > +}
> > +
> > +/*
> > + * @drc : device DRC targetting which the async hcalls to be made.
> > + * token : The continue token to be used for tracking as recived from
> > + * spapr_drc_get_new_async_hcall_token
> > + * @func() : the worker function which needs to be executed asynchronously
> > + * @data : data to be passed to the asynchronous function. Worker is supposed
> > + * to free/cleanup the data that is passed here
>
> It'd be cleaner to pass a completion callback and have free/cleanup handled there.
>
> > + */
> > +void spapr_drc_run_async_hcall(SpaprDrc *drc, uint64_t token,
> > + SpaprDrcAsyncHcallWorkerFunc *func, void *data)
> > +{
> > + SpaprDrcDeviceAsyncHCallState *state;
> > +
> > + qemu_mutex_lock(&drc->async_hcall_states_lock);
> > + QLIST_FOREACH(state, &drc->async_hcall_states, node) {
> > + if (state->continue_token == token) {
> > + state->func = func;
> > + state->data = data;
> > + qemu_thread_create(&state->thread, "sPAPR Async HCALL",
> > + spapr_drc_async_hcall_runner, state,
> > + QEMU_THREAD_JOINABLE);
>
> qemu_thread_create() exits on failure, it shouldn't be called on
> a guest triggerable path, eg. a buggy guest could call it up to
> the point that pthread_create() returns EAGAIN.
>
> Please use a thread pool (see thread_pool_submit_aio()). This takes care
> of all the thread housekeeping for you in a safe way, and it provides a
> completion callback API. The implementation could then be just about
> having two lists: one for pending requests (fed here) and one for
> completed requests (fed by the completion callback).
>
> > + break;
> > + }
> > + }
> > + qemu_mutex_unlock(&drc->async_hcall_states_lock);
> > +}
> > +
> > +/*
> > + * spapr_drc_finish_async_hcalls
> > + * Waits for all pending async requests to complete
> > + * thier execution and free the states
> > + */
> > +static void spapr_drc_finish_async_hcalls(SpaprDrc *drc)
> > +{
> > + SpaprDrcDeviceAsyncHCallState *state, *next;
> > +
> > + if (QLIST_EMPTY(&drc->async_hcall_states)) {
> > + return;
> > + }
> > +
> > + qemu_mutex_lock(&drc->async_hcall_states_lock);
> > + QLIST_FOREACH_SAFE(state, &drc->async_hcall_states, node, next) {
> > + qemu_thread_join(&state->thread);
>
> With a thread-pool, you'd just need to aio_poll() until the pending list
> is empty and then clear the completed list.
>
> > + QLIST_REMOVE(state, node);
> > + g_free(state);
> > + }
> > + qemu_mutex_unlock(&drc->async_hcall_states_lock);
> > +}
> > +
> > +/*
> > + * spapr_drc_get_async_hcall_status
> > + * Fetches the status of the hcall worker and returns H_BUSY
> > + * if the worker is still running.
> > + */
> > +int spapr_drc_get_async_hcall_status(SpaprDrc *drc, uint64_t token)
> > +{
> > + int ret = H_PARAMETER;
> > + SpaprDrcDeviceAsyncHCallState *state, *node;
> > +
> > + qemu_mutex_lock(&drc->async_hcall_states_lock);
> > + QLIST_FOREACH_SAFE(state, &drc->async_hcall_states, node, node) {
> > + if (state->continue_token == token) {
> > + if (state->pending) {
> > + ret = H_BUSY;
> > + break;
> > + } else {
> > + ret = state->hcall_ret;
> > + qemu_thread_join(&state->thread);
>
> Like for qemu_thread_create(), the guest shouldn't be responsible for
> thread housekeeping. Getting the hcall status should just be about
> finding the token in the pending or completed lists.
>
> > + QLIST_REMOVE(state, node);
> > + g_free(state);
> > + break;
> > + }
> > + }
> > + }
> > + qemu_mutex_unlock(&drc->async_hcall_states_lock);
> > +
> > + return ret;
> > +}
> > +
> > void spapr_drc_reset(SpaprDrc *drc)
> > {
> > SpaprDrcClass *drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
> > @@ -448,6 +591,7 @@ void spapr_drc_reset(SpaprDrc *drc)
> > drc->ccs_offset = -1;
> > drc->ccs_depth = -1;
> > }
> > + spapr_drc_finish_async_hcalls(drc);
> > }
> >
> > static bool spapr_drc_unplug_requested_needed(void *opaque)
> > @@ -558,6 +702,7 @@ SpaprDrc *spapr_dr_connector_new(Object *owner, const char *type,
> > drc->owner = owner;
> > prop_name = g_strdup_printf("dr-connector[%"PRIu32"]",
> > spapr_drc_index(drc));
> > +
>
> Unrelated change.
>
> > object_property_add_child(owner, prop_name, OBJECT(drc));
> > object_unref(OBJECT(drc));
> > qdev_realize(DEVICE(drc), NULL, NULL);
> > @@ -577,6 +722,10 @@ static void spapr_dr_connector_instance_init(Object *obj)
> > object_property_add(obj, "fdt", "struct", prop_get_fdt,
> > NULL, NULL, NULL);
> > drc->state = drck->empty_state;
> > +
> > + qemu_mutex_init(&drc->async_hcall_states_lock);
> > + QLIST_INIT(&drc->async_hcall_states);
> > +
>
> Empty line not needed.
>
> > }
> >
> > static void spapr_dr_connector_class_init(ObjectClass *k, void *data)
> > diff --git a/include/hw/ppc/spapr_drc.h b/include/hw/ppc/spapr_drc.h
> > index 165b281496..77f6e4386c 100644
> > --- a/include/hw/ppc/spapr_drc.h
> > +++ b/include/hw/ppc/spapr_drc.h
> > @@ -18,6 +18,7 @@
> > #include "sysemu/runstate.h"
> > #include "hw/qdev-core.h"
> > #include "qapi/error.h"
> > +#include "block/thread-pool.h"
> >
> > #define TYPE_SPAPR_DR_CONNECTOR "spapr-dr-connector"
> > #define SPAPR_DR_CONNECTOR_GET_CLASS(obj) \
> > @@ -168,6 +169,21 @@ typedef enum {
> > SPAPR_DRC_STATE_PHYSICAL_CONFIGURED = 8,
> > } SpaprDrcState;
> >
> > +typedef struct SpaprDrc SpaprDrc;
> > +
> > +typedef int SpaprDrcAsyncHcallWorkerFunc(void *opaque);
> > +typedef struct SpaprDrcDeviceAsyncHCallState {
> > + uint64_t continue_token;
> > + bool pending;
> > +
> > + int hcall_ret;
> > + SpaprDrcAsyncHcallWorkerFunc *func;
> > + void *data;
> > +
> > + QemuThread thread;
> > +
> > + QLIST_ENTRY(SpaprDrcDeviceAsyncHCallState) node;
> > +} SpaprDrcDeviceAsyncHCallState;
> > typedef struct SpaprDrc {
> > /*< private >*/
> > DeviceState parent;
> > @@ -182,6 +198,10 @@ typedef struct SpaprDrc {
> > int ccs_offset;
> > int ccs_depth;
> >
> > + /* async hcall states */
> > + QemuMutex async_hcall_states_lock;
> > + QLIST_HEAD(, SpaprDrcDeviceAsyncHCallState) async_hcall_states;
> > +
> > /* device pointer, via link property */
> > DeviceState *dev;
> > bool unplug_requested;
> > @@ -241,6 +261,11 @@ void spapr_drc_detach(SpaprDrc *drc);
> > /* Returns true if a hot plug/unplug request is pending */
> > bool spapr_drc_transient(SpaprDrc *drc);
> >
> > +uint64_t spapr_drc_get_new_async_hcall_token(SpaprDrc *drc);
> > +void spapr_drc_run_async_hcall(SpaprDrc *drc, uint64_t token,
> > + SpaprDrcAsyncHcallWorkerFunc, void *data);
> > +int spapr_drc_get_async_hcall_status(SpaprDrc *drc, uint64_t token);
> > +
> > static inline bool spapr_drc_unplug_requested(SpaprDrc *drc)
> > {
> > return drc->unplug_requested;
> >
> >
> >
>
--
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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