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[Pal/Linux-SGX] Exitless: let untrusted RPC threads sleep

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Previously, the Exitless feature forced all untrusted RPC threads
to spin forever while waiting for new syscall requests from enclave
threads. This led to constant high CPU utilization even on idle
workloads. This commit adds simple logic for RPC threads to first
spin for a while and then perform short nanosleeps. This heuristic
significantly reduces CPU utilization at the penalty of increased
latency in case when syscall request arrives when RPC thread is
sleeping ("warm-up" of RPC thread).
This commit is contained in:
Dmitrii Kuvaiskii
2020-06-18 09:19:02 -07:00
parent 2b3f3e5925
commit 4d764cb005
1 changed files with 22 additions and 1 deletions
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Pal/src/host/Linux-SGX/sgx_enclave.c
+22 -1
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@@ -724,13 +724,34 @@ static int rpc_thread_loop(void* arg) {
g_rpc_queue->rpc_threads_cnt++;
spinlock_unlock(&g_rpc_queue->lock);
static const uint64_t SPIN_ATTEMPTS_MAX = 10000; /* rather arbitrary */
static const uint64_t SLEEP_TIME_MAX = 100000000; /* nanoseconds (0.1 seconds) */
static const uint64_t SLEEP_TIME_STEP = SLEEP_TIME_MAX / 100; /* 100 steps before capped */
/* no races possible since vars are thread-local and RPC threads don't receive signals */
uint64_t spin_attempts = 0;
uint64_t sleep_time = 0;
while (1) {
rpc_request_t* req = rpc_dequeue(g_rpc_queue);
if (!req) {
cpu_pause();
if (spin_attempts == SPIN_ATTEMPTS_MAX) {
if (sleep_time < SLEEP_TIME_MAX)
sleep_time += SLEEP_TIME_STEP;
struct timespec tv = {.tv_sec = 0, .tv_nsec = sleep_time};
(void)INLINE_SYSCALL(nanosleep, 2, &tv, /*rem=*/NULL);
} else {
spin_attempts++;
cpu_pause();
}
continue;
}
/* new request came, reset spin/sleep heuristics */
spin_attempts = 0;
sleep_time = 0;
/* call actual function and notify awaiting enclave thread when done */
sgx_ocall_fn_t f = ocall_table[req->ocall_index];
req->result = f(req->buffer);