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[PAL/LinuxSGX] fast-clock desc type cleanups
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Signed-off-by: Jonathan Shamir <jsham92@gmail.com>
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jonathan-sha committed Apr 8, 2024
1 parent aa8f0aa commit 4927cdb
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Showing 2 changed files with 79 additions and 92 deletions.
110 changes: 57 additions & 53 deletions pal/src/host/linux-sgx/utils/fast_clock.c
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Original file line number Diff line number Diff line change
Expand Up @@ -66,10 +66,10 @@
*
* To achieve the above, we use the following data structures.
*
* 1. fast_clock_timepoint_t - this contains all the internal state needed by FastClock to
* 1. fast_clock_timepoint - this contains all the internal state needed by FastClock to
* calculate the time as discussed above. FastClock internally has *two* timepoints, which
* are used in round-robin (alternating).
* 2. fast_clock_desc_t - this is read and written to atomically, which is how the lockless
* 2. fast_clock_desc - this is read and written to atomically, which is how the lockless
* thread safety is implemented. The descriptor contains:
* - The current "state" of the FastClock state machine.
* - The round-robin index of the timepoint that is currently in use.
Expand Down Expand Up @@ -104,9 +104,23 @@
#define RDTSC_CALIBRATION_TIME ((uint64_t)1 * TIME_US_IN_S)
#define RDTSC_RECALIBRATION_INTERVAL ((uint64_t)120 * TIME_US_IN_S)

fast_clock_t g_fast_clock = {
.atomic_descriptor = { .state = FC_STATE_INIT, .flags = FC_FLAGS_INIT },
.time_points = { [0 ... _FC_NUM_TIMEPOINTS-1] = {
typedef enum
{
FC_STATE_RDTSC,
FC_STATE_RDTSC_RECALIBRATE,
FC_STATE_CALIBRATING,
FC_STATE_INIT,

FC_STATE_RDTSC_DISABLED,
} fast_clock_state;

fast_clock g_fast_clock = {
.atomic_descriptor = {
.state = FC_STATE_INIT,
.timepoint_index = 0,
.state_changing = 0,
},
.time_points = { [0 ... FC_NUM_TIMEPOINTS-1] = {
.clock_freq = 0,
.tsc0 = 0,
.t0_usec = 0,
Expand All @@ -115,75 +129,65 @@ fast_clock_t g_fast_clock = {
};


static inline uint16_t timepoint_index(fast_clock_desc_t curr)
{
return (curr.flags & FC_FLAGS_TIMEPOINT_MASK);
}

static inline fast_clock_desc_t advance_state(fast_clock_desc_t curr, fast_clock_state_t new_state, bool advance_timepoint)
static inline fast_clock_desc advance_state(fast_clock_desc curr, fast_clock_state new_state, bool advance_timepoint)
{
fast_clock_desc_t new_descriptor;
new_descriptor.state = new_state;
uint16_t new_tp_index = timepoint_index(curr);
if (advance_timepoint) {
new_tp_index = (new_tp_index + 1) % FC_FLAGS_NUM_TIMEPOINTS;
}
new_descriptor.flags = new_tp_index;
fast_clock_desc new_descriptor = {
.state = new_state,
.timepoint_index = advance_timepoint ? curr.timepoint_index + 1 : curr.timepoint_index,
.state_changing = 0,
};
return new_descriptor;
}

static inline bool is_expired(const fast_clock_timepoint_t* timepoint, uint64_t now_usec)
static inline bool is_expired(const fast_clock_timepoint* timepoint, uint64_t now_usec)
{
return (timepoint->expiration_usec < now_usec);
}

static inline void calc_time(const fast_clock_timepoint_t* timepoint, uint64_t* time_usec)
static inline void calc_time(const fast_clock_timepoint* timepoint, uint64_t* time_usec)
{
uint64_t tsc = get_tsc();
uint64_t dtsc = tsc - timepoint->tsc0;
uint64_t dt_usec = (dtsc * TIME_US_IN_S) / timepoint->clock_freq;
*time_usec = timepoint->t0_usec + dt_usec;
}

static inline void reset_clock_frequency(fast_clock_timepoint_t* timepoint, uint64_t tsc, uint64_t time_usec)
static inline void reset_clock_frequency(fast_clock_timepoint* timepoint, uint64_t tsc, uint64_t time_usec)
{
// calculate clock frequency in Hz
uint64_t dt_usec = time_usec - timepoint->t0_usec;
uint64_t dtsc = tsc - timepoint->tsc0;
timepoint->clock_freq = (dtsc * TIME_US_IN_S) / dt_usec;
}

static inline long reset_timepoint(fast_clock_timepoint_t* timepoint)
static inline long reset_timepoint(fast_clock_timepoint* timepoint)
{
int ret = ocall_gettime(&timepoint->t0_usec, &timepoint->tsc0);
return ret;
}

static inline void reset_expiration(fast_clock_timepoint_t* timepoint, uint64_t next_expiration)
static inline void reset_expiration(fast_clock_timepoint* timepoint, uint64_t next_expiration)
{
timepoint->expiration_usec = timepoint->t0_usec + next_expiration;
}

static inline bool set_change_state_guard(fast_clock_t* fast_clock, fast_clock_desc_t descriptor)
static inline bool set_change_state_guard(fast_clock* fast_clock, fast_clock_desc descriptor)
{
if ((descriptor.flags & FC_FLAGS_STATE_CHANGING) != 0) {
if (descriptor.state_changing != 0) {
return false;
}

fast_clock_desc_t state_change_guard_desc = {
.state = descriptor.state,
.flags = descriptor.flags | FC_FLAGS_STATE_CHANGING,
};

fast_clock_desc state_change_guard_desc = descriptor;
state_change_guard_desc.state_changing = 1;
return __atomic_compare_exchange_n(
&fast_clock->atomic_descriptor.desc, &descriptor.desc, state_change_guard_desc.desc,
/*weak=*/false, __ATOMIC_RELAXED, __ATOMIC_RELAXED
);
}

static inline fast_clock_timepoint_t* get_timepoint(fast_clock_t* fast_clock, fast_clock_desc_t descriptor)
static inline fast_clock_timepoint* get_timepoint(fast_clock* fast_clock, fast_clock_desc descriptor)
{
return &fast_clock->time_points[timepoint_index(descriptor)];
return &fast_clock->time_points[descriptor.timepoint_index];
}

static bool is_rdtsc_available(void) {
Expand Down Expand Up @@ -215,20 +219,20 @@ static int handle_state_rdtsc_disabled(uint64_t* time_usec)
return ocall_gettime(time_usec, NULL);
}

static int handle_state_init(fast_clock_t* fast_clock, fast_clock_desc_t descriptor, uint64_t* time_usec)
static int handle_state_init(fast_clock* fast_clock, fast_clock_desc descriptor, uint64_t* time_usec)
{
if (!set_change_state_guard(fast_clock, descriptor)) {
return handle_state_rdtsc_disabled(time_usec);
}

if (!is_rdtsc_available()) {
fast_clock_desc_t next_desc = advance_state(descriptor, FC_STATE_RDTSC_DISABLED, false);
fast_clock_desc next_desc = advance_state(descriptor, FC_STATE_RDTSC_DISABLED, false);
__atomic_store_n(&fast_clock->atomic_descriptor.desc, next_desc.desc, __ATOMIC_RELAXED);
return handle_state_rdtsc_disabled(time_usec);
}

fast_clock_desc_t next_desc = advance_state(descriptor, FC_STATE_CALIBRATING, false);
fast_clock_timepoint_t* timepoint = get_timepoint(fast_clock, next_desc);
fast_clock_desc next_desc = advance_state(descriptor, FC_STATE_CALIBRATING, false);
fast_clock_timepoint* timepoint = get_timepoint(fast_clock, next_desc);
int ret = reset_timepoint(timepoint);

// gettimeofday failed - restore descriptor
Expand All @@ -246,7 +250,7 @@ static int handle_state_init(fast_clock_t* fast_clock, fast_clock_desc_t descrip
return ret;
}

static int handle_state_calibrating(fast_clock_t* fast_clock, fast_clock_desc_t descriptor, uint64_t* time_usec)
static int handle_state_calibrating(fast_clock* fast_clock, fast_clock_desc descriptor, uint64_t* time_usec)
{
// all callers in this state will perform an OCALL - no need to set the change_state_guard before OCALLing
uint64_t tmp_tsc = 0;
Expand All @@ -255,23 +259,23 @@ static int handle_state_calibrating(fast_clock_t* fast_clock, fast_clock_desc_t
return ret;
}

fast_clock_timepoint_t* timepoint = get_timepoint(fast_clock, descriptor);
fast_clock_timepoint* timepoint = get_timepoint(fast_clock, descriptor);
if (!is_expired(timepoint, *time_usec) || !set_change_state_guard(fast_clock, descriptor)) {
return ret;
}

// calculate the clock_freq and advance state
reset_clock_frequency(timepoint, tmp_tsc, *time_usec);
reset_expiration(timepoint, RDTSC_RECALIBRATION_INTERVAL);
fast_clock_desc_t new_desc = advance_state(descriptor, FC_STATE_RDTSC, false);
fast_clock_desc new_desc = advance_state(descriptor, FC_STATE_RDTSC, false);
__atomic_store_n(&fast_clock->atomic_descriptor.desc, new_desc.desc, __ATOMIC_RELEASE);

return ret;
}

static inline int handle_state_rdtsc(fast_clock_t* fast_clock, fast_clock_desc_t descriptor, uint64_t* time_usec, bool force_new_timepoint)
static inline int handle_state_rdtsc(fast_clock* fast_clock, fast_clock_desc descriptor, uint64_t* time_usec, bool force_new_timepoint)
{
fast_clock_timepoint_t* timepoint = get_timepoint(fast_clock, descriptor);
fast_clock_timepoint* timepoint = get_timepoint(fast_clock, descriptor);

// fast path - calculate time with rdtsc
calc_time(timepoint, time_usec);
Expand All @@ -281,8 +285,8 @@ static inline int handle_state_rdtsc(fast_clock_t* fast_clock, fast_clock_desc_t
}

// acquire the state_change_guard and prepare the next state (get new ground truth timepoint)
fast_clock_desc_t next_desc = advance_state(descriptor, FC_STATE_RDTSC_RECALIBRATE, true);
fast_clock_timepoint_t* next_timepoint = get_timepoint(fast_clock, next_desc);
fast_clock_desc next_desc = advance_state(descriptor, FC_STATE_RDTSC_RECALIBRATE, true);
fast_clock_timepoint* next_timepoint = get_timepoint(fast_clock, next_desc);

int ret = reset_timepoint(next_timepoint);
if (ret != 0) {
Expand All @@ -299,9 +303,9 @@ static inline int handle_state_rdtsc(fast_clock_t* fast_clock, fast_clock_desc_t
return ret;
}

static inline int handle_state_rdtsc_recalibrate(fast_clock_t* fast_clock, fast_clock_desc_t descriptor, uint64_t* time_usec)
static inline int handle_state_rdtsc_recalibrate(fast_clock* fast_clock, fast_clock_desc descriptor, uint64_t* time_usec)
{
fast_clock_timepoint_t* timepoint = get_timepoint(fast_clock, descriptor);
fast_clock_timepoint* timepoint = get_timepoint(fast_clock, descriptor);

// fast path - calculate time with rdtsc
calc_time(timepoint, time_usec);
Expand All @@ -318,15 +322,15 @@ static inline int handle_state_rdtsc_recalibrate(fast_clock_t* fast_clock, fast_

reset_clock_frequency(timepoint, tsc, *time_usec);
reset_expiration(timepoint, RDTSC_RECALIBRATION_INTERVAL);
fast_clock_desc_t next_desc = advance_state(descriptor, FC_STATE_RDTSC, false);
fast_clock_desc next_desc = advance_state(descriptor, FC_STATE_RDTSC, false);
__atomic_store_n(&fast_clock->atomic_descriptor.desc, next_desc.desc, __ATOMIC_RELEASE);

return ret;
}

int fast_clock_get_time(fast_clock_t* fast_clock, uint64_t* time_usec, bool force_new_timepoint)
int fast_clock_get_time(fast_clock* fast_clock, uint64_t* time_usec, bool force_new_timepoint)
{
fast_clock_desc_t descriptor = {
fast_clock_desc descriptor = {
.desc = __atomic_load_n(&fast_clock->atomic_descriptor.desc, __ATOMIC_ACQUIRE),
};
switch (descriptor.state)
Expand All @@ -345,23 +349,23 @@ int fast_clock_get_time(fast_clock_t* fast_clock, uint64_t* time_usec, bool forc
}
}

bool fast_clock_is_enabled(const fast_clock_t* fast_clock)
bool fast_clock_is_enabled(const fast_clock* fast_clock)
{
fast_clock_desc_t descriptor = {
fast_clock_desc descriptor = {
.desc = __atomic_load_n(&fast_clock->atomic_descriptor.desc, __ATOMIC_RELAXED),
};
return (descriptor.state != FC_STATE_RDTSC_DISABLED);
}

void fast_clock_disable(fast_clock_t* fast_clock)
void fast_clock_disable(fast_clock* fast_clock)
{
/* We need to busy-loop until the state change guard is acquired here - since fast-clock
* might be in the midst of transitioning states. We can't simply store the DISABLED state. */
fast_clock_desc_t descriptor;
fast_clock_desc descriptor;
do {
descriptor.desc = __atomic_load_n(&fast_clock->atomic_descriptor.desc, __ATOMIC_ACQUIRE);
} while(!set_change_state_guard(fast_clock, descriptor));

fast_clock_desc_t disabled_desc = advance_state(descriptor, FC_STATE_RDTSC_DISABLED, false);
fast_clock_desc disabled_desc = advance_state(descriptor, FC_STATE_RDTSC_DISABLED, false);
__atomic_store_n(&fast_clock->atomic_descriptor.desc, disabled_desc.desc, __ATOMIC_RELEASE);
}
61 changes: 22 additions & 39 deletions pal/src/host/linux-sgx/utils/fast_clock.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2,62 +2,45 @@

#include <stdint.h>
#include <stdbool.h>
#include "api.h"


enum fast_clock_state_e
{
FC_STATE_RDTSC,
FC_STATE_RDTSC_RECALIBRATE,
FC_STATE_CALIBRATING,
FC_STATE_INIT,

FC_STATE_RDTSC_DISABLED,
};
typedef uint16_t fast_clock_state_t;

#define _FC_NUM_TIMEPOINT_BITS (1)
#define _FC_NUM_TIMEPOINTS (1<<_FC_NUM_TIMEPOINT_BITS)

enum fast_clock_flags_e
{
FC_FLAGS_INIT = 0,

FC_FLAGS_TIMEPOINT_MASK = _FC_NUM_TIMEPOINTS - 1,
FC_FLAGS_NUM_TIMEPOINTS = _FC_NUM_TIMEPOINTS,

FC_FLAGS_STATE_CHANGING = 0x8000,
};
typedef uint16_t fast_clock_flags_t;
#define FC_NUM_TIMEPOINTS (1<<_FC_NUM_TIMEPOINT_BITS)

typedef union
{
#pragma pack(push, 1)
struct
{
fast_clock_state_t state;
fast_clock_flags_t flags;
uint16_t state : 4;
uint16_t timepoint_index : _FC_NUM_TIMEPOINT_BITS;
uint16_t _pad0 : (16 - _FC_NUM_TIMEPOINT_BITS - 5);
uint16_t state_changing : 1;
};
#pragma pack(pop)

uint32_t desc;
} fast_clock_desc_t;
uint16_t desc;
} fast_clock_desc;

static_assert(_FC_NUM_TIMEPOINT_BITS >= 1, "timepoint_index must have at minimum 1-bit");
static_assert(_FC_NUM_TIMEPOINT_BITS + 5 <= 16, "timepoint_index uses too many bits");
static_assert(sizeof(fast_clock_desc) == sizeof(uint16_t), "fast_clock_desc size mismatch");

typedef struct fast_clock_timepoint_s
typedef struct
{
uint64_t clock_freq;
uint64_t tsc0;
uint64_t t0_usec;
uint64_t expiration_usec;
} fast_clock_timepoint_t;
} fast_clock_timepoint;

typedef struct fast_clock_s
typedef struct
{
fast_clock_desc_t atomic_descriptor;
fast_clock_timepoint_t time_points[FC_FLAGS_NUM_TIMEPOINTS];
} fast_clock_t;
fast_clock_desc atomic_descriptor;
fast_clock_timepoint time_points[FC_NUM_TIMEPOINTS];
} fast_clock;

extern fast_clock_t g_fast_clock;
extern fast_clock g_fast_clock;

int fast_clock_get_time(fast_clock_t* fast_clock, uint64_t* time_micros, bool force_new_timepoint);
bool fast_clock_is_enabled(const fast_clock_t* fast_clock);
void fast_clock_disable(fast_clock_t* fast_clock);
int fast_clock_get_time(fast_clock* fast_clock, uint64_t* time_micros, bool force_new_timepoint);
bool fast_clock_is_enabled(const fast_clock* fast_clock);
void fast_clock_disable(fast_clock* fast_clock);

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