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Date:   Thu, 15 Jul 2021 17:47:01 -0300
From:   Arnaldo Carvalho de Melo <acme@kernel.org>
To:     Riccardo Mancini <rickyman7@gmail.com>
Cc:     Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
        Ian Rogers <irogers@google.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Jiri Olsa <jolsa@redhat.com>, linux-kernel@vger.kernel.org,
        linux-perf-users@vger.kernel.org
Subject: Re: [RFC PATCH 06/10] perf workqueue: introduce workqueue struct
Message-ID: <YPCexbV0O1PoNCJF@kernel.org>
References: <cover.1626177381.git.rickyman7@gmail.com>
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 <d39def9e5c3edd6292d86c90036fd79a2406db1d.camel@gmail.com>
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Em Thu, Jul 15, 2021 at 06:49:57PM +0200, Riccardo Mancini escreveu:
> Hi Arnaldo,
> thanks again for having a look at this patchset!
> 
> On Wed, 2021-07-14 at 12:22 -0300, Arnaldo Carvalho de Melo wrote:
> > Em Tue, Jul 13, 2021 at 02:11:17PM +0200, Riccardo Mancini escreveu:
> > > This patch adds the workqueue definition, along with simple creation and
> > > destruction functions.
> > > Furthermore, a simple subtest is added.
> > > 
> > > A workqueue is attached to a pool, on which it executes its workers.
> > > Next patches will introduce workers.
> > > 
> > > Signed-off-by: Riccardo Mancini <rickyman7@gmail.com>
> > > 
> <SNIP>
> > > +
> > > +/**
> > > + * create_workqueue - create a workqueue associated to @pool
> > > + *
> > > + * Only one workqueue can execute on a pool at a time.
> > > + */
> > > +struct workqueue_struct *create_workqueue(struct threadpool_struct *pool)
> > 
> > I wonder if we should use the exact same kernel signature and not pass a
> > threadpool, essentially having just one threadpool in tools/perf/ that
> > is used by create_workqueue(void)?
> 
> I wondered the same thing, but I thought that we'd need it to be dynamically
> created to prevent spawning threads at the beginning that might not even be
> used.
> I think this could be a follow-up patch.

I see your point.

My practice is to use the perf convention for things that don't come
from the kernel, and if we do as I suggested, tooling will probably not
even see this threadpool struct, i.e. just the workqueue APIs are
exposed and workqueue_create() will notice that a threadpool is not yet
created, doing its creation behind tooling's back.

- Arnaldo
 
> Thanks,
> Riccardo
> 
> > 
> > > +{
> > > +???????int err;
> > > +???????struct workqueue_struct *wq = malloc(sizeof(struct
> > > workqueue_struct));
> > > +
> > > +
> > > +???????err = pthread_mutex_init(&wq->lock, NULL);
> > > +???????if (err)
> > > +???????????????goto out_free_wq;
> > > +
> > > +???????err = pthread_cond_init(&wq->idle_cond, NULL);
> > > +???????if (err)
> > > +???????????????goto out_destroy_mutex;
> > > +
> > > +???????wq->pool = NULL;
> > > +???????INIT_LIST_HEAD(&wq->busy_list);
> > > +???????INIT_LIST_HEAD(&wq->idle_list);
> > > +
> > > +???????INIT_LIST_HEAD(&wq->pending);
> > > +
> > > +???????err = pipe(wq->msg_pipe);
> > > +???????if (err)
> > > +???????????????goto out_destroy_cond;
> > > +
> > > +???????wq->task.fn = worker_thread;
> > > +
> > > +???????err = attach_threadpool_to_workqueue(wq, pool);
> > > +???????if (err)
> > > +???????????????goto out_destroy_cond;
> > > +
> > > +???????wq->status = WORKQUEUE_STATUS__READY;
> > > +
> > > +???????return wq;
> > > +
> > > +out_destroy_cond:
> > > +???????pthread_cond_destroy(&wq->idle_cond);
> > > +out_destroy_mutex:
> > > +???????pthread_mutex_destroy(&wq->lock);
> > > +out_free_wq:
> > > +???????free(wq);
> > > +???????return NULL;
> > > +}
> > > +
> > > +/**
> > > + * destroy_workqueue - stop @wq workers and destroy @wq
> > > + */
> > > +int destroy_workqueue(struct workqueue_struct *wq)
> > > +{
> > > +???????int err = 0, ret;
> > > +
> > > +???????ret = detach_threadpool_from_workqueue(wq);
> > > +???????if (ret) {
> > > +???????????????pr_err("workqueue: error detaching from threadpool.\n");
> > > +???????????????err = -1;
> > > +???????}
> > > +
> > > +???????ret = pthread_mutex_destroy(&wq->lock);
> > > +???????if (ret) {
> > > +???????????????err = -1;
> > > +???????????????pr_err("workqueue: error pthread_mutex_destroy: %s\n",
> > > +???????????????????????strerror(errno));
> > > +???????}
> > > +
> > > +???????ret = pthread_cond_destroy(&wq->idle_cond);
> > > +???????if (ret) {
> > > +???????????????err = -1;
> > > +???????????????pr_err("workqueue: error pthread_cond_destroy: %s\n",
> > > +???????????????????????strerror(errno));
> > > +???????}
> > > +
> > > +???????ret = close(wq->msg_pipe[0]);
> > > +???????if (ret) {
> > > +???????????????err = -1;
> > > +???????????????pr_err("workqueue: error close msg_pipe[0]: %s\n",
> > > +???????????????????????strerror(errno));
> > > +???????}
> > > +
> > > +???????ret = close(wq->msg_pipe[1]);
> > > +???????if (ret) {
> > > +???????????????err = -1;
> > > +???????????????pr_err("workqueue: error close msg_pipe[1]: %s\n",
> > > +???????????????????????strerror(errno));
> > > +???????}
> > > +
> > > +???????free(wq);
> > > +
> > > +???????return err;
> > > +}
> > > +
> > > +/**
> > > + * workqueue_nr_threads - get size of threadpool underlying @wq
> > > + */
> > > +int workqueue_nr_threads(struct workqueue_struct *wq)
> > > +{
> > > +???????return threadpool_size(wq->pool);
> > > +}
> > > diff --git a/tools/perf/util/workqueue/workqueue.h
> > > b/tools/perf/util/workqueue/workqueue.h
> > > new file mode 100644
> > > index 0000000000000000..86ec1d69274f41db
> > > --- /dev/null
> > > +++ b/tools/perf/util/workqueue/workqueue.h
> > > @@ -0,0 +1,24 @@
> > > +/* SPDX-License-Identifier: GPL-2.0 */
> > > +#ifndef __WORKQUEUE_WORKQUEUE_H
> > > +#define __WORKQUEUE_WORKQUEUE_H
> > > +
> > > +#include <stdlib.h>
> > > +#include <sys/types.h>
> > > +#include <linux/list.h>
> > > +#include "threadpool.h"
> > > +
> > > +struct work_struct;
> > > +typedef void (*work_func_t)(struct work_struct *work);
> > > +
> > > +struct work_struct {
> > > +???????struct list_head entry;
> > > +???????work_func_t func;
> > > +};
> > > +
> > > +struct workqueue_struct;
> > > +
> > > +extern struct workqueue_struct *create_workqueue(struct threadpool_struct
> > > *pool);
> > > +extern int destroy_workqueue(struct workqueue_struct *wq);
> > > +
> > > +extern int workqueue_nr_threads(struct workqueue_struct *wq);
> > > +#endif /* __WORKQUEUE_WORKQUEUE_H */
> > > -- 
> > > 2.31.1
> > > 
> > 
> 
> 

-- 

- Arnaldo