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Message-ID: <cf0067475311633b91fc22eeb7215c5dac79031e.camel@gmail.com>
Date: Thu, 15 Jul 2021 18:31:07 +0200
From: Riccardo Mancini <rickyman7@...il.com>
To: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc: Ian Rogers <irogers@...gle.com>,
Namhyung Kim <namhyung@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Mark Rutland <mark.rutland@....com>,
Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
linux-perf-users@...r.kernel.org,
Alexey Bayduraev <alexey.v.bayduraev@...ux.intel.com>
Subject: Re: [RFC PATCH 01/10] perf workqueue: threadpool creation and
destruction
Hi Arnaldo,
thanks for reviewing the patch!
On Wed, 2021-07-14 at 11:16 -0300, Arnaldo Carvalho de Melo wrote:
<SNIP>
> > +
> > +enum threadpool_status {
> > + THREADPOOL_STATUS__STOPPED, /* no threads */
> > + THREADPOOL_STATUS__ERROR, /* errors */
> > + THREADPOOL_STATUS__MAX
> > +};
> > +
> > +struct threadpool_struct {
>
> Can this be just 'struct threadpool'? I think its descriptive enough:
I agree, but I wanted to keep the naming consistent between workqueue.c and
threadpool.c.
>
> > + int nr_threads; /* number of threads in the
> > pool */
> > + struct thread_struct *threads; /* array of threads in the
> > pool */
> > + struct task_struct *current_task; /* current executing
> > function
> > */
> > + enum threadpool_status status; /* current status of the
> > pool
> > */
> > +};
> > +
> > +struct thread_struct {
> > + int idx; /* idx of thread in pool-
> > > threads */
> > + pid_t tid; /* tid of thread */
> > + struct threadpool_struct *pool; /* parent threadpool */
> > + struct {
> > + int from[2]; /* messages from thread
> > (acks)
> > */
> > + int to[2]; /* messages to thread
> > (commands) */
> > + } pipes;
> > +};
>
> This one, since we have already a 'struct thread' in tools/perf, to
> represent a PERF_RECORD_FORK, perhaps we can call it 'struct
> threadpool_entry'?
Agreed.
>
> > +
> > +/**
> > + * init_pipes - initialize all pipes of @thread
> > + */
> > +static void init_pipes(struct thread_struct *thread)
> > +{
> > + thread->pipes.from[0] = -1;
> > + thread->pipes.from[1] = -1;
> > + thread->pipes.to[0] = -1;
> > + thread->pipes.to[1] = -1;
> > +}
> > +
> > +/**
> > + * open_pipes - open all pipes of @thread
> > + */
> > +static int open_pipes(struct thread_struct *thread)
>
> Here please:
>
> threadpool_entry__open_pipes()
>
> Its longer, but helps with ctags/cscope navigation and we can go
> directly to it via:
>
> :ta threadpool_entry__open_p<TAB>
>
> While 'ta: open_pipes' may bo to various places where this idiom is
> used.
Agreed.
<SNIP>
> > +/**
> > + * create_threadpool - create a fixed threadpool with @n_threads threads
> > + */
> > +struct threadpool_struct *create_threadpool(int n_threads)
>
>
> Is this already something the kernel has and thus we should keep the
> naming? I couldn't find it in the kernel, so please name it:
>
> struct threadpool *threadpool__new(int nthreads)
As before, I did this to keep consistency with workqueue.
Since this threadpool+workqueue can be a standalone library, I preferred to keep
the naming consistent inside it, instead of making it consistent with perf (this
is what I was referring to in the cover letter, not just the workqueue API).
What do you think?
I also prefer perf's naming conventions, but it'd feel strange to use two
different naming conventions inside the same library.
>
> > +{
> > + int ret, t;
> > + struct threadpool_struct *pool = malloc(sizeof(*pool));
> > +
> > + if (!pool) {
> > + pr_err("threadpool: cannot allocate pool: %s\n",
> > + strerror(errno));o
>
> Humm, pr_err() at this level isn't appropriate, please make callers
> complain.
ok.
>
> > + return NULL;
> > + }
> > +
> > + if (n_threads <= 0) {
> > + pr_err("threadpool: invalid number of threads: %d\n",
> > + n_threads);
>
> pr_debug()
ok
>
> > + goto out_free_pool;
> > + }
> > +
> > + pool->nr_threads = n_threads;
> > + pool->current_task = NULL;
> > +
> > + pool->threads = malloc(n_threads * sizeof(*pool->threads));
> > + if (!pool->threads) {
> > + pr_err("threadpool: cannot allocate threads: %s\n",
> > + strerror(errno));
> > + 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;
> > + init_pipes(&pool->threads[t]);
> > + }
> > +
> > + for (t = 0; t < n_threads; t++) {
> > + ret = open_pipes(&pool->threads[t]);
> > + if (ret)
> > + goto out_close_pipes;
> > + }
> > +
> > + pool->status = THREADPOOL_STATUS__STOPPED;
> > +
> > + return pool;
> > +
> > +out_close_pipes:
> > + for (t = 0; t < n_threads; t++)
> > + close_pipes(&pool->threads[t]);
> > +
> > + free(pool->threads);
> > +out_free_pool:
> > + free(pool);
> > + return NULL;
>
> Here we can use ERR_PTR()/PTR_ERR() to let the caller know what was the
> problem, i.e. we can ditch all the pr_err/pr_debug(), etc and instead
> have a threadpool__strerror(struct threadpool *pool, int err) like we
> have for 'struct evsel', please take a look at evsel__open_strerror().
Thanks, I'll have a look at it.
So, what I sould do is not use pr_* higher than debug inside library code and
return meaningful errors through PR_ERR, right?
>
>
> > +}
> > +
> > +/**
> > + * destroy_threadpool - free the @pool and all its resources
> > + */
> > +void destroy_threadpool(struct threadpool_struct *pool)
>
>
> void threadpool__delete(struct threadpool *pool)
> > +{
> > + int t;
> > +
> > + if (!pool)
> > + return;
> > +
> > + WARN_ON(pool->status != THREADPOOL_STATUS__STOPPED
> > + && pool->status != THREADPOOL_STATUS__ERROR);
> > +
> > + for (t = 0; t < pool->nr_threads; t++)
> > + close_pipes(&pool->threads[t]);
>
> reset pool->threads[t] to -1
already inside close_pipes. I agree it might be confusing without the
threadpool_entry__ prefix.
>
> > +
> > + free(pool->threads);
>
> zfree
In general, when should I use zfree instead of free?
>
> > + free(pool);
> > +}
> > +
> > +/**
> > + * threadpool_size - get number of threads in the threadpool
> > + */
> > +int threadpool_size(struct threadpool_struct *pool)
>
> threadpool__size()
ok
Thanks,
Riccardo
>
> > +{
> > + 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..2b9388c768a0b588
> > --- /dev/null
> > +++ b/tools/perf/util/workqueue/threadpool.h
> > @@ -0,0 +1,19 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef __WORKQUEUE_THREADPOOL_H
> > +#define __WORKQUEUE_THREADPOOL_H
> > +
> > +struct threadpool_struct;
> > +struct task_struct;
> > +
> > +typedef void (*task_func_t)(int tidx, struct task_struct *task);
> > +
> > +struct task_struct {
> > + task_func_t fn;
> > +};
> > +
> > +extern struct threadpool_struct *create_threadpool(int n_threads);
> > +extern void destroy_threadpool(struct threadpool_struct *pool);
> > +
> > +extern int threadpool_size(struct threadpool_struct *pool);
> > +
> > +#endif /* __WORKQUEUE_THREADPOOL_H */
> > --
> > 2.31.1
> >
>
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