sim-se: (Re)add support for retrying system calls.
The previous incarnation of this support used faults to make the CPU
reexecute the system call instruction again and again to prevent
emulating/passing through blocking system calls from blocking gem5 as
a whole. That support was accidentally removed a while ago. This new
version suspends the thread context executing the system call, and
periodically wakes it up to retry using a periodically scheduled event.
Jira Issue: https://gem5.atlassian.net/browse/GEM5-1123
Change-Id: I155fa8205d7ea45e3d102216aeca6ee1979a522f
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/54205
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>
diff --git a/src/sim/syscall_desc.cc b/src/sim/syscall_desc.cc
index 7427f41..d293167 100644
--- a/src/sim/syscall_desc.cc
+++ b/src/sim/syscall_desc.cc
@@ -30,6 +30,7 @@
#include "sim/syscall_desc.hh"
#include "base/types.hh"
+#include "sim/eventq.hh"
#include "sim/syscall_debug_macros.hh"
namespace gem5
@@ -45,12 +46,58 @@
SyscallReturn retval = executor(this, tc);
if (retval.needsRetry()) {
- DPRINTF_SYSCALL(Base, "Needs retry.\n", name());
- } else if (retval.suppressed()) {
+ // Suspend this ThreadContext while the syscall is pending.
+ tc->suspend();
+
+ DPRINTF_SYSCALL(Base, "%s needs retry.\n", name());
+ setupRetry(tc);
+ return;
+ }
+
+ handleReturn(tc, retval);
+}
+
+void
+SyscallDesc::retrySyscall(ThreadContext *tc)
+{
+ DPRINTF_SYSCALL(Base, "Retrying %s...\n", dumper(name(), tc));
+
+ SyscallReturn retval = executor(this, tc);
+
+ if (retval.needsRetry()) {
+ DPRINTF_SYSCALL(Base, "%s still needs retry.\n", name());
+ setupRetry(tc);
+ return;
+ }
+
+ // We're done retrying, so reactivate this ThreadContext.
+ tc->activate();
+
+ handleReturn(tc, retval);
+}
+
+void
+SyscallDesc::setupRetry(ThreadContext *tc)
+{
+ // Create an event which will retry the system call later.
+ auto retry = [this, tc]() { retrySyscall(tc); };
+ auto *event = new EventFunctionWrapper(retry, name(), true);
+
+ // Schedule it in about 100 CPU cycles. That will give other contexts
+ // a chance to execute a bit of code before trying again.
+ auto *cpu = tc->getCpuPtr();
+ curEventQueue()->schedule(event,
+ curTick() + cpu->cyclesToTicks(Cycles(100)));
+}
+
+void
+SyscallDesc::handleReturn(ThreadContext *tc, const SyscallReturn &ret)
+{
+ if (ret.suppressed()) {
DPRINTF_SYSCALL(Base, "No return value.\n", name());
} else {
- returnInto(tc, retval);
- DPRINTF_SYSCALL(Base, "Returned %d.\n", retval.encodedValue());
+ returnInto(tc, ret);
+ DPRINTF_SYSCALL(Base, "Returned %d.\n", ret.encodedValue());
}
}
diff --git a/src/sim/syscall_desc.hh b/src/sim/syscall_desc.hh
index 6ded904..e89cf49 100644
--- a/src/sim/syscall_desc.hh
+++ b/src/sim/syscall_desc.hh
@@ -95,11 +95,16 @@
_name(name), _num(num), executor(exec), dumper(dump)
{}
+ void retrySyscall(ThreadContext *tc);
+
private:
/** System call name (e.g., open, mmap, clone, socket, etc.) */
std::string _name;
int _num;
+ void setupRetry(ThreadContext *tc);
+ void handleReturn(ThreadContext *tc, const SyscallReturn &ret);
+
/** Mechanism for ISAs to connect to the emul function definitions */
Executor executor;
Dumper dumper;