Hi Namhyung,
thanks for the review!

On Fri, 2021-08-06 at 19:24 -0700, Namhyung Kim wrote:

Hi Riccardo,

On Fri, Jul 30, 2021 at 8:34 AM Riccardo Mancini [off-list ref] wrote:

quoted

The workqueue library is made up by two components:
 - threadpool: handles the lifetime of the threads
 - workqueue: handles work distribution among the threads

This first patch introduces the threadpool, starting from its creation
and destruction functions.
Thread management is based on the prototype from Alexey:
https://lore.kernel.org/lkml/cover.1625227739.git.alexey.v.bayduraev@linux.intel.com/ (local)

Each thread in the threadpool executes the same function (aka task)
with a different argument tidx.
Threads use a pair of pipes to communicate with the main process.
The threadpool is static (all threads will be spawned at the same time).
Future work could include making it resizable and adding affinity support
(as in Alexey prototype).

Suggested-by: Alexey Bayduraev <redacted>
Signed-off-by: Riccardo Mancini <redacted>
---
 tools/perf/util/Build                  |   1 +
 tools/perf/util/workqueue/Build        |   1 +
 tools/perf/util/workqueue/threadpool.c | 208 +++++++++++++++++++++++++
 tools/perf/util/workqueue/threadpool.h |  30 ++++
 4 files changed, 240 insertions(+)
 create mode 100644 tools/perf/util/workqueue/Build
 create mode 100644 tools/perf/util/workqueue/threadpool.c
 create mode 100644 tools/perf/util/workqueue/threadpool.h

diff --git a/tools/perf/util/Build b/tools/perf/util/Build
index 2d4fa13041789cd6..c7b09701661c869d 100644
--- a/tools/perf/util/Build
+++ b/tools/perf/util/Build

@@ -180,6 +180,7 @@ perf-$(CONFIG_LIBBABELTRACE) += data-convert-bt.o

 perf-y += data-convert-json.o

 perf-y += scripting-engines/
+perf-y += workqueue/

 perf-$(CONFIG_ZLIB) += zlib.o
 perf-$(CONFIG_LZMA) += lzma.o

diff --git a/tools/perf/util/workqueue/Build

b/tools/perf/util/workqueue/Build
new file mode 100644
index 0000000000000000..8b72a6cd4e2cba0d

--- /dev/null
+++ b/tools/perf/util/workqueue/Build

@@ -0,0 +1 @@
+perf-y += threadpool.o

diff --git a/tools/perf/util/workqueue/threadpool.c

b/tools/perf/util/workqueue/threadpool.c
new file mode 100644
index 0000000000000000..0004ce606d5fa73d

--- /dev/null
+++ b/tools/perf/util/workqueue/threadpool.c

@@ -0,0 +1,208 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include "debug.h"
+#include <asm/bug.h>
+#include <linux/zalloc.h>
+#include <linux/string.h>
+#include <linux/err.h>
+#include <linux/kernel.h>
+#include "threadpool.h"
+
+enum threadpool_status {
+       THREADPOOL_STATUS__STOPPED,             /* no threads */
+       THREADPOOL_STATUS__ERROR,               /* errors */
+       THREADPOOL_STATUS__MAX
+};
+
+struct threadpool {
+       int                     nr_threads;     /* number of threads in the

pool */
+       struct threadpool_entry *threads;       /* array of threads in the
pool */
+       struct task_struct      *current_task;  /* current executing
function */
+       enum threadpool_status  status;         /* current status of the
pool */

Better to move to below the nr_threads for alignment.

ack

quoted

+};
+
+struct threadpool_entry {
+       int                             idx;    /* idx of thread in pool-

quoted

threads */

+       pid_t                           tid;    /* tid of thread */
+       struct threadpool               *pool;  /* parent threadpool */
+       struct {
+               int ack[2];                     /* messages from thread
(acks) */
+               int cmd[2];                     /* messages to thread
(commands) */
+       } pipes;
+};
+
+/**
+ * threadpool_entry__init_pipes - initialize all pipes of @thread
+ */
+static void threadpool_entry__init_pipes(struct threadpool_entry *thread)
+{
+       thread->pipes.ack[0] = -1;
+       thread->pipes.ack[1] = -1;
+       thread->pipes.cmd[0] = -1;
+       thread->pipes.cmd[1] = -1;
+}
+
+/**
+ * threadpool_entry__open_pipes - open all pipes of @thread
+ */
+static int threadpool_entry__open_pipes(struct threadpool_entry *thread)
+{
+       if (pipe(thread->pipes.ack)) {
+               pr_debug2("threadpool: failed to create comm pipe 'from':
%s\n",
+                       strerror(errno));
+               return -ENOMEM;
+       }
+
+       if (pipe(thread->pipes.cmd)) {
+               pr_debug2("threadpool: failed to create comm pipe 'to':
%s\n",
+                       strerror(errno));
+               close(thread->pipes.ack[0]);
+               thread->pipes.ack[0] = -1;
+               close(thread->pipes.ack[1]);
+               thread->pipes.ack[1] = -1;

Maybe you don't need to do it here if the caller handles it already ...

oops, thanks.

quoted

+               return -ENOMEM;
+       }
+
+       return 0;
+}
+
+/**
+ * threadpool_entry__close_pipes - close all communication pipes of @thread
+ */
+static void threadpool_entry__close_pipes(struct threadpool_entry *thread)
+{
+       if (thread->pipes.ack[0] != -1) {
+               close(thread->pipes.ack[0]);
+               thread->pipes.ack[0] = -1;
+       }
+       if (thread->pipes.ack[1] != -1) {
+               close(thread->pipes.ack[1]);
+               thread->pipes.ack[1] = -1;
+       }
+       if (thread->pipes.cmd[0] != -1) {
+               close(thread->pipes.cmd[0]);
+               thread->pipes.cmd[0] = -1;
+       }
+       if (thread->pipes.cmd[1] != -1) {
+               close(thread->pipes.cmd[1]);
+               thread->pipes.cmd[1] = -1;
+       }
+}
+
+/**
+ * threadpool__new - create a fixed threadpool with @n_threads threads
+ */
+struct threadpool *threadpool__new(int n_threads)
+{
+       int ret, err, t;
+       struct threadpool *pool = malloc(sizeof(*pool));
+
+       if (!pool) {
+               pr_debug2("threadpool: cannot allocate pool: %s\n",
+                       strerror(errno));
+               err = -ENOMEM;
+               goto out_return;
+       }
+
+       if (n_threads <= 0) {
+               pr_debug2("threadpool: invalid number of threads: %d\n",
+                       n_threads);
+               err = -EINVAL;
+               goto out_free_pool;

Isn't' it natural to check it before the allocation?

It sure is, thanks.

quoted

+       }
+
+       pool->nr_threads = n_threads;
+       pool->current_task = NULL;
+
+       pool->threads = calloc(n_threads, sizeof(*pool->threads));
+       if (!pool->threads) {
+               pr_debug2("threadpool: cannot allocate threads: %s\n",
+                       strerror(errno));
+               err = -ENOMEM;
+               goto out_free_pool;
+       }
+
+       for (t = 0; t < n_threads; t++) {
+               pool->threads[t].idx = t;
+               pool->threads[t].tid = -1;
+               pool->threads[t].pool = pool;
+               threadpool_entry__init_pipes(&pool->threads[t]);
+       }
+
+       for (t = 0; t < n_threads; t++) {
+               ret = threadpool_entry__open_pipes(&pool->threads[t]);
+               if (ret) {
+                       err = -ret;
+                       goto out_close_pipes;

... like this.  But threadpool_entry__open_pipes() already
returns a negative.

Yeah, I made some confusion with signs in this version, because I first wanted
to use positive for errnos and negative for custom errors but it didn't sound
like a good idea, so then I reverted to only negative errors, using the offset
for the custom errors.
I will have a better look at all return codes.

quoted

+               }
+       }
+
+       pool->status = THREADPOOL_STATUS__STOPPED;
+
+       return pool;
+
+out_close_pipes:
+       for (t = 0; t < n_threads; t++)
+               threadpool_entry__close_pipes(&pool->threads[t]);
+
+       zfree(&pool->threads);
+out_free_pool:
+       free(pool);
+out_return:
+       return ERR_PTR(err);
+}
+
+/**
+ * threadpool__strerror - print message regarding given @err in @pool
+ *
+ * Buffer size should be at least THREADPOOL_STRERR_BUFSIZE bytes.
+ */
+int threadpool__strerror(struct threadpool *pool __maybe_unused, int err,
char *buf, size_t size)
+{
+       char sbuf[STRERR_BUFSIZE], *emsg;
+
+       emsg = str_error_r(err, sbuf, sizeof(sbuf));
+       return scnprintf(buf, size, "Error: %s.\n", emsg);
+}
+
+/**
+ * threadpool__new_strerror - print message regarding @err_ptr
+ *
+ * Buffer size should be at least THREADPOOL_STRERR_BUFSIZE bytes.
+ */
+int threadpool__new_strerror(struct threadpool *err_ptr, char *buf, size_t
size)
+{
+       return threadpool__strerror(err_ptr, PTR_ERR(err_ptr), buf, size);
+}

Why two different functions?

Since when new fails you don't have a err number, just an err_ptr so it's not
very clear how to call threadpool__strerror. Therefore I made a wrapper to
remove any ambiguity.

quoted

+
+/**
+ * threadpool__delete - free the @pool and all its resources
+ */
+void threadpool__delete(struct threadpool *pool)
+{
+       int t;
+
+       if (IS_ERR_OR_NULL(pool))
+               return;
+
+       WARN_ON(pool->status != THREADPOOL_STATUS__STOPPED
+               && pool->status != THREADPOOL_STATUS__ERROR);
+
+       for (t = 0; t < pool->nr_threads; t++)
+               threadpool_entry__close_pipes(&pool->threads[t]);
+
+       zfree(&pool->threads);
+       free(pool);
+}
+
+/**
+ * threadpool__size - get number of threads in the threadpool
+ */
+int threadpool__size(struct threadpool *pool)
+{
+       return pool->nr_threads;
+}

diff --git a/tools/perf/util/workqueue/threadpool.h

b/tools/perf/util/workqueue/threadpool.h
new file mode 100644
index 0000000000000000..fb18aa32fb64f671

--- /dev/null
+++ b/tools/perf/util/workqueue/threadpool.h

@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __WORKQUEUE_THREADPOOL_H
+#define __WORKQUEUE_THREADPOOL_H
+
+struct threadpool;
+struct task_struct;

You can just move the definition here.

quoted

+
+typedef void (*task_func_t)(int tidx, struct task_struct *task);
+
+struct task_struct {
+       task_func_t fn;
+};

I thought it was not allowed, since task_func_t refers to task_struct and
viceversa.
I will try to remove it if possible.

quoted

+
+extern struct threadpool *threadpool__new(int n_threads);
+extern void threadpool__delete(struct threadpool *pool);
+
+extern int threadpool__start(struct threadpool *pool);
+extern int threadpool__stop(struct threadpool *pool);
+
+extern int threadpool__execute(struct threadpool *pool, struct task_struct
*task);
+extern int threadpool__wait(struct threadpool *pool);

These are not defined yet.

Oops, they must've leaked from the 3rd patch.

Thanks,
Riccardo

quoted

+
+extern int threadpool__size(struct threadpool *pool);
+
+/* Error management */
+#define THREADPOOL_STRERR_BUFSIZE (128+STRERR_BUFSIZE)
+extern int threadpool__strerror(struct threadpool *pool, int err, char
*buf, size_t size);
+extern int threadpool__new_strerror(struct threadpool *err_ptr, char *buf,
size_t size);
+
+#endif /* __WORKQUEUE_THREADPOOL_H */
--
2.31.1