On Thu, Mar 24, 2022 at 9:31 AM Tyler Retzlaff
<roret...@linux.microsoft.com> wrote:
> > diff --git a/lib/eal/common/eal_common_thread.c
> > b/lib/eal/common/eal_common_thread.c
> > index 684bea166c..256de91abc 100644
> > --- a/lib/eal/common/eal_common_thread.c
> > +++ b/lib/eal/common/eal_common_thread.c
> > @@ -9,6 +9,7 @@
> > #include <assert.h>
> > #include <string.h>
> >
> > +#include <rte_eal_trace.h>
> > #include <rte_errno.h>
> > #include <rte_lcore.h>
> > #include <rte_log.h>
> > @@ -163,6 +164,77 @@ __rte_thread_uninit(void)
> > RTE_PER_LCORE(_lcore_id) = LCORE_ID_ANY;
> > }
> >
> > +/* main loop of threads */
> > +__rte_noreturn void *
> > +eal_thread_loop(__rte_unused void *arg)
> > +{
> > + char cpuset[RTE_CPU_AFFINITY_STR_LEN];
> > + pthread_t thread_id = pthread_self();
> > + unsigned int lcore_id;
> > + int ret;
> > +
> > + /* retrieve our lcore_id from the configuration structure */
> > + RTE_LCORE_FOREACH_WORKER(lcore_id) {
> > + if (thread_id == lcore_config[lcore_id].thread_id)
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> i can see that in practice this isn't a problem since the linux
> implementation of pthread_create(3) stores to pthread_t *thread before
> executing start_routine.
>
> but strictly speaking i don't think the pthread_create api contractually
> guarantees that the thread id is stored before start_routine runs. so this
> is relying on an internal implementation detail.
>
> https://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_create.html
>
> "Upon successful completion, pthread_create() shall store the ID of the
> created thread in the location referenced by thread."
>
> https://man7.org/linux/man-pages/man3/pthread_create.3.html
>
> "Before returning, a successful call to pthread_create() stores
> the ID of the new thread in the buffer pointed to by thread; this
> identifier is used to refer to the thread in subsequent calls to
> other pthreads functions."
>
> it doesn't really say when it does this in relation to start_routine running.
> depends how hair splitty you want to be about it. but since you're revamping
> the code you might be interested in addressing it.
I had wondered about this part too in the past.
I don't see a reason to keep this loop (even considering baremetal,
since this code is within the linux implementation of EAL).
And this comment seems a good reason to cleanup the code (like simply
pass lcore_id via arg).
Something like:
Author: David Marchand <david.march...@redhat.com>
Date: Thu Mar 24 11:29:46 2022 +0100
eal: cleanup lcore hand-over from main thread
As noted by Tyler, there is nothing in the pthread API that strictly
guarantees that the new thread won't start running eal_thread_loop
before pthread_create writes to &lcore_config[xx].thread_id.
Rather than rely on thread id, the main thread can directly pass the
worker thread lcore.
Signed-off-by: David Marchand <david.march...@redhat.com>
diff --git a/lib/eal/common/eal_common_thread.c
b/lib/eal/common/eal_common_thread.c
index 256de91abc..962b7e9ac4 100644
--- a/lib/eal/common/eal_common_thread.c
+++ b/lib/eal/common/eal_common_thread.c
@@ -166,26 +166,17 @@ __rte_thread_uninit(void)
/* main loop of threads */
__rte_noreturn void *
-eal_thread_loop(__rte_unused void *arg)
+eal_thread_loop(void *arg)
{
+ unsigned int lcore_id = (uintptr_t)arg;
char cpuset[RTE_CPU_AFFINITY_STR_LEN];
- pthread_t thread_id = pthread_self();
- unsigned int lcore_id;
int ret;
- /* retrieve our lcore_id from the configuration structure */
- RTE_LCORE_FOREACH_WORKER(lcore_id) {
- if (thread_id == lcore_config[lcore_id].thread_id)
- break;
- }
- if (lcore_id == RTE_MAX_LCORE)
- rte_panic("cannot retrieve lcore id\n");
-
__rte_thread_init(lcore_id, &lcore_config[lcore_id].cpuset);
ret = eal_thread_dump_current_affinity(cpuset, sizeof(cpuset));
RTE_LOG(DEBUG, EAL, "lcore %u is ready (tid=%zx;cpuset=[%s%s])\n",
- lcore_id, (uintptr_t)thread_id, cpuset,
+ lcore_id, (uintptr_t)pthread_self(), cpuset,
ret == 0 ? "" : "...");
rte_eal_trace_thread_lcore_ready(lcore_id, cpuset);
diff --git a/lib/eal/common/eal_thread.h b/lib/eal/common/eal_thread.h
index b08dcf34b5..0fde33e70c 100644
--- a/lib/eal/common/eal_thread.h
+++ b/lib/eal/common/eal_thread.h
@@ -11,7 +11,7 @@
* basic loop of thread, called for each thread by eal_init().
*
* @param arg
- * opaque pointer
+ * The lcore_id (passed as an integer) of this worker thread.
*/
__rte_noreturn void *eal_thread_loop(void *arg);
diff --git a/lib/eal/freebsd/eal.c b/lib/eal/freebsd/eal.c
index 80bc3d25e0..a6b20960f2 100644
--- a/lib/eal/freebsd/eal.c
+++ b/lib/eal/freebsd/eal.c
@@ -810,7 +810,7 @@ rte_eal_init(int argc, char **argv)
/* create a thread for each lcore */
ret = pthread_create(&lcore_config[i].thread_id, NULL,
- eal_thread_loop, NULL);
+ eal_thread_loop, (void *)(uintptr_t)i);
if (ret != 0)
rte_panic("Cannot create thread\n");
diff --git a/lib/eal/linux/eal.c b/lib/eal/linux/eal.c
index 8a405d1d59..1ef263434a 100644
--- a/lib/eal/linux/eal.c
+++ b/lib/eal/linux/eal.c
@@ -1145,7 +1145,7 @@ rte_eal_init(int argc, char **argv)
/* create a thread for each lcore */
ret = pthread_create(&lcore_config[i].thread_id, NULL,
- eal_thread_loop, NULL);
+ eal_thread_loop, (void *)(uintptr_t)i);
if (ret != 0)
rte_panic("Cannot create thread\n");
diff --git a/lib/eal/windows/eal.c b/lib/eal/windows/eal.c
index ca3c41aaa7..1874f9f6d7 100644
--- a/lib/eal/windows/eal.c
+++ b/lib/eal/windows/eal.c
@@ -420,7 +420,7 @@ rte_eal_init(int argc, char **argv)
lcore_config[i].state = WAIT;
/* create a thread for each lcore */
- if (eal_thread_create(&lcore_config[i].thread_id) != 0)
+ if (eal_thread_create(&lcore_config[i].thread_id, i) != 0)
rte_panic("Cannot create thread\n");
ret = pthread_setaffinity_np(lcore_config[i].thread_id,
sizeof(rte_cpuset_t), &lcore_config[i].cpuset);
diff --git a/lib/eal/windows/eal_thread.c b/lib/eal/windows/eal_thread.c
index de1c0078a5..704781a83c 100644
--- a/lib/eal/windows/eal_thread.c
+++ b/lib/eal/windows/eal_thread.c
@@ -71,13 +71,14 @@ eal_thread_ack_command(void)
/* function to create threads */
int
-eal_thread_create(pthread_t *thread)
+eal_thread_create(pthread_t *thread, unsigned int lcore_id)
{
HANDLE th;
th = CreateThread(NULL, 0,
(LPTHREAD_START_ROUTINE)(ULONG_PTR)eal_thread_loop,
- NULL, 0, (LPDWORD)thread);
+ (LPVOID)(uintptr_t)lcore_id, 0,
+ (LPDWORD)thread);
if (!th)
return -1;
But seeing how this code has been there from day 1, I would not
request a backport.
--
David Marchand
