No need for shadow to notify plugin that shmem operations are done (#1132)

sporksmith · web-flow · commit 0e13d3f4e3c9 · 2021-03-02T10:15:20.000-06:00
thread_preload was notifying the shim shmem operations were done before
sending back the results of each syscall. The shim doesn't do anything
in response to this other than send back an acknowledgment message.

Removing this drops execution time from 20s to 17s in the "workload"
syscall microbenchmark with 512 hosts.
diff --git a/src/main/host/thread_preload.c b/src/main/host/thread_preload.c
@@ -283,19 +283,6 @@ SysCallCondition* threadpreload_resume(Thread* base) {
 
                 _threadpreload_flushPtrs(thread);
 
-                // We've handled the syscall, so we notify that we are done
-                // with shmem IPC
-                ShimEvent ipc_complete_ev = {
-                    .event_id = SHD_SHIM_EVENT_SHMEM_COMPLETE,
-                };
-
-                shimevent_sendEventToPlugin(thread->ipc_blk.p, &ipc_complete_ev);
-
-                ShimEvent resp = {0};
-                shimevent_recvEventFromPlugin(thread->ipc_blk.p, &resp);
-
-                utility_assert(resp.event_id == SHD_SHIM_EVENT_SHMEM_COMPLETE);
-
                 ShimEvent shim_result;
                 if (result.state == SYSCALL_DONE) {
                     // Now send the result of the syscall
diff --git a/src/shim/preload_syscall.c b/src/shim/preload_syscall.c
@@ -134,7 +134,6 @@ static SysCallReg _shadow_syscall_event(const ShimEvent* syscall_event) {
                 shim_shmemHandleWrite(&res);
                 shim_shmemNotifyComplete(ipc_blk.p);
                 break;
-            case SHD_SHIM_EVENT_SHMEM_COMPLETE: shim_shmemNotifyComplete(ipc_blk.p); break;
             default: {
                 error("Got unexpected event %d", res.event_id);
                 abort();
@@ -211,4 +210,4 @@ long syscall(long n, ...) {
     }
     va_end(args);
     return rv;
-}
+}
