Hi Feifei,
>
> The variable "wrk_cmd" is a signal to control threads from running and
> stopping. When worker lcores load "wrk_cmd == WRK_CMD_RUN", they start
> running and when worker lcores load "wrk_cmd == WRK_CMD_STOP", they
> stop.
>
> For the wmb in test_mt1, no storing operations must keep the order
> after storing "wrk_cmd". Thus the wmb is unnecessary.
I think there is a bug in my original code, we should do smp_wmb() *before*
setting wrk_cmd, not after:
/* launch on all workers */
RTE_LCORE_FOREACH_WORKER(lc) {
arg[lc].rng = r;
arg[lc].stats = init_stat;
rte_eal_remote_launch(test, &arg[lc], lc);
}
/* signal worker to start test */
+ rte_smp_wmb();
wrk_cmd = WRK_CMD_RUN;
- rte_smp_wmb();
usleep(run_time * US_PER_S);
I still think we'd better have some synchronisation here.
Otherwise what would prevent compiler and/or cpu to update wrk_cmd out of order
(before _init_ phase is completed)?
We probably can safely assume no reordering from the compiler here,
as we have function calls straight before and after 'wrk_cmd = WRK_CMD_RUN;'
But for consistency and easier maintenance, I still think it is better
to have something here, after all it is not performance critical pass.
> For the rmb in test_worker, the parameters have been prepared when
> worker lcores call "test_worker". It is unnessary to wait wrk_cmd to be
> loaded, then the parameters can be loaded, So the rmb can be removed.
It is not only about parameters loading, it is to prevent worker core to start
too early.
As I understand, your goal is to get rid of rte_smp_*() calls.
Might be better to replace such places here with _atomic_ semantics.
Then, as I can see, we also can get rid of 'volatile' fo wrk_cmd.
> In the meanwhile, fix a typo. The note above storing "stop" into
> "wrk_cmd" should be "stop test" rather than "start test".
>
> Signed-off-by: Feifei Wang <feifei.wa...@arm.com>
> Reviewed-by: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.w...@arm.com>
> ---
> app/test/test_ring_stress_impl.h | 5 +----
> 1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/app/test/test_ring_stress_impl.h
> b/app/test/test_ring_stress_impl.h
> index f9ca63b90..384555ef9 100644
> --- a/app/test/test_ring_stress_impl.h
> +++ b/app/test/test_ring_stress_impl.h
> @@ -198,7 +198,6 @@ test_worker(void *arg, const char *fname, int32_t prcs)
> fill_ring_elm(&loc_elm, lc);
>
> while (wrk_cmd != WRK_CMD_RUN) {
> - rte_smp_rmb();
> rte_pause();
> }
>
> @@ -357,13 +356,11 @@ test_mt1(int (*test)(void *))
>
> /* signal worker to start test */
> wrk_cmd = WRK_CMD_RUN;
> - rte_smp_wmb();
>
> usleep(run_time * US_PER_S);
>
> - /* signal worker to start test */
> + /* signal worker to stop test */
> wrk_cmd = WRK_CMD_STOP;
> - rte_smp_wmb();
>
> /* wait for workers and collect stats. */
> mc = rte_lcore_id();
> --
> 2.17.1
