Re: [RFC PATCH v2 01/10] perf workqueue: threadpool creation and destruction

[Riccardo Mancini <rickyman7@gmail.com>]

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 <rickyman7@gmail.com> wrote:
> > 
> > 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/
> > 
> > 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 <alexey.v.bayduraev@linux.intel.com>
> > Signed-off-by: Riccardo Mancini <rickyman7@gmail.com>
> > ---
> >  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

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

> 
> > +               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.

> 
> > +       }
> > +
> > +       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.

> 
> > +               }
> > +       }
> > +
> > +       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.
> 
> > +
> > +/**
> > + * 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.
> 
> > +
> > +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.

> > +
> > +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

> 
> > +
> > +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
> >