Re: [PATCH] tools/memory-model: Document herd7 (internal) representation
From: Hernan Ponce de Leon
Date: Mon May 27 2024 - 08:23:23 EST
On 5/24/2024 5:13 PM, Andrea Parri wrote:
tools/memory-model/ and herdtool7 are closely linked: the latter is
responsible for (pre)processing each C-like macro of a litmus test,
and for providing the LKMM with a set of events, or "representation",
corresponding to the given macro. Provide herd-representation.txt
to document the representation of synchronization macros, following
their "classification" in Documentation/atomic_t.txt.
Suggested-by: Hernan Ponce de Leon <hernan.poncedeleon@xxxxxxxxxxxxxxx>
Signed-off-by: Andrea Parri <parri.andrea@xxxxxxxxx>
---
- Leaving srcu_{up,down}_read() and smp_mb__after_srcu_read_unlock() for
the next version.
- Limiting to "add" and "and" ops (skipping similar/same representations
for "sub", "inc", "dec", "or", "xor", "andnot").
- While preparing this submission, I recalled that atomic_add_unless()
is not listed in the .def file. I can't remember the reason for this
omission though.
- While checking the information below using herd7, I've observed some
"strange" behavior with spin_is_locked() (perhaps, unsurprisingly...);
IAC, that's also excluded from this table/submission.
.../Documentation/herd-representation.txt | 81 +++++++++++++++++++
1 file changed, 81 insertions(+)
create mode 100644 tools/memory-model/Documentation/herd-representation.txt
diff --git a/tools/memory-model/Documentation/herd-representation.txt b/tools/memory-model/Documentation/herd-representation.txt
new file mode 100644
index 0000000000000..94d0d0a9eee50
--- /dev/null
+++ b/tools/memory-model/Documentation/herd-representation.txt
@@ -0,0 +1,81 @@
+ ---------------------------------------------------------------------------
+ | C macro | Events |
+ ---------------------------------------------------------------------------
+ | Non-RMW ops | |
+ ---------------------------------------------------------------------------
+ | READ_ONCE | R[once] |
+ | atomic_read | (as in the previous row) |
+ | WRITE_ONCE | W[once] |
+ | atomic_set | |
+ | smp_load_acquire | R[acquire] |
+ | atomic_read_acquire | |
+ | smp_store_release | W[release] |
+ | atomic_set_release | |
+ | smp_store_mb | W[once] ->po F[mb] |
I expect this one to be hard-coded in herd7 source code, but I cannot
find it. Can you give me a pointer?
In fact, dartagnan uses W[Mb] ... another clear example of the need for
documentation as this one.
+ | smp_mb | F[mb] |
+ | smp_rmb | F[rmb] |
+ | smp_wmb | F[wmb] |
+ | smp_mb__before_atomic | F[before-atomic] |
+ | smp_mb__after_atomic | F[after-atomic] |
+ | spin_unlock | UL |
+ | smp_mb__after_spinlock | F[after-spinlock] |
+ | smp_mb__after_unlock_lock | F[after-unlock-lock] |
+ | rcu_read_lock | F[rcu-lock] |
+ | rcu_read_unlock | F[rcu-unlock] |
+ | synchronize_rcu | F[sync-rcu] |
+ | rcu_dereference | R[once] |
+ | rcu_assign_pointer | W[release] |
+ | srcu_read_lock | R[srcu-lock] |
+ | srcu_read_unlock | W[srcu-unlock] |
+ | synchronize_srcu | SRCU[sync-srcu] |
+ ---------------------------------------------------------------------------
+ | RMW ops w/o return value | |
+ ---------------------------------------------------------------------------
+ | atomic_add | R*[noreturn] ->rmw W*[once] |
+ | atomic_and | |
+ | spin_lock | LKR ->lk-rmw LKW |
What about spin_unlock?
+ ---------------------------------------------------------------------------
+ | RMW ops w/ return value | |
+ ---------------------------------------------------------------------------
+ | atomic_add_return | F[mb] ->po R*[once] |
+ | | ->rmw W*[once] ->po F[mb] |
+ | atomic_fetch_add | |
+ | atomic_fetch_and | |
+ | atomic_xchg | |
+ | xchg | |
+ | atomic_add_negative | |
+ | atomic_add_return_relaxed | R*[once] ->rmw W*[once] |
+ | atomic_fetch_add_relaxed | |
+ | atomic_fetch_and_relaxed | |
+ | atomic_xchg_relaxed | |
+ | xchg_relaxed | |
+ | atomic_add_negative_relaxed | |
+ | atomic_add_return_acquire | R*[acquire] ->rmw W*[once] |
+ | atomic_fetch_add_acquire | |
+ | atomic_fetch_and_acquire | |
+ | atomic_xchg_acquire | |
+ | xchg_acquire | |
+ | atomic_add_negative_acquire | |
+ | atomic_add_return_release | R*[once] ->rmw W*[release] |
+ | atomic_fetch_add_release | |
+ | atomic_fetch_and_release | |
+ | atomic_xchg_release | |
+ | xchg_release | |
+ | atomic_add_negative_release | |
+ ---------------------------------------------------------------------------
+ | Conditional RMW ops | |
+ ---------------------------------------------------------------------------
+ | atomic_cmpxchg | On success: F[mb] ->po R*[once] |
+ | | ->rmw W*[once] ->po F[mb] |
+ | | On failure: R*[once] |
+ | cmpxchg | |
+ | atomic_add_unless | |
+ | atomic_cmpxchg_relaxed | On success: R*[once] ->rmw W*[once] |
+ | | On failure: R*[once] |
+ | atomic_cmpxchg_acquire | On success: R*[acquire] ->rmw W*[once] |
+ | | On failure: R*[once] |
+ | atomic_cmpxchg_release | On success: R*[once] ->rmw W*[release] |
+ | | On failure: R*[once] |
+ | spin_trylock | On success: LKR ->lk-rmw LKW |
+ | | On failure: LF |
+ ---------------------------------------------------------------------------
I found the extra spaces in the failure case very hard to read. Any
particular reason why you went with this format?
Hernan