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

[Namhyung Kim <namhyung@kernel.org>]

Hi Riccardo and Arnaldo,

On Wed, Jul 14, 2021 at 7:16 AM Arnaldo Carvalho de Melo
<acme@kernel.org> wrote:
>
> Em Tue, Jul 13, 2021 at 02:11:12PM +0200, Riccardo Mancini escreveu:
> > 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 | 175 +++++++++++++++++++++++++
> >  tools/perf/util/workqueue/threadpool.h |  19 +++
> >  4 files changed, 196 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..70c67569f956a3e2
> > --- /dev/null
> > +++ b/tools/perf/util/workqueue/threadpool.c
> > @@ -0,0 +1,175 @@
> > +// 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 "threadpool.h"
> > +
> > +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:
>
> > +     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 */

Does this mean it can only have a single function to run?
Why do we need it?


> > +     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) */

It can be confusing if you think from the main thread.
Maybe 'ack' and 'cmd' would be better.


> > +     } 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'?

I think we can even use 'worker' instead of 'thread' but it requires
huge renaming and conflicts so I won't insist on it strongly.  :)

Thanks,
Namhyung