linux-kernel - Re: [RFC PATCH 03/10] perf workqueue: add threadpool start and stop functions

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Message-ID: <YPGz2xTCa/EkvrxY@kernel.org>
Date:   Fri, 16 Jul 2021 13:29:15 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Riccardo Mancini <rickyman7@...il.com>
Cc:     Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Jiri Olsa <jolsa@...hat.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-perf-users <linux-perf-users@...r.kernel.org>,
        Alexey Bayduraev <alexey.v.bayduraev@...ux.intel.com>
Subject: Re: [RFC PATCH 03/10] perf workqueue: add threadpool start and stop
 functions

Em Fri, Jul 16, 2021 at 03:53:58PM +0200, Riccardo Mancini escreveu:
> On Thu, 2021-07-15 at 16:48 -0700, Namhyung Kim wrote:
> > On Tue, Jul 13, 2021 at 5:11 AM Riccardo Mancini <rickyman7@...il.com> wrote:
> > > +++ b/tools/perf/util/workqueue/threadpool.c
> > [SNIP]
> > > +/**
> > > + * wait_thread - receive ack from thread
> > > + *
> > > + * NB: call only from main thread!
> > > + */
> > > +static int wait_thread(struct thread_struct *thread)
> > > +{
> > > +       int res;
> > > +       enum thread_msg msg = THREAD_MSG__UNDEFINED;
> > > +
> > > +       res = read(thread->pipes.from[0], &msg, sizeof(msg));
> > > +       if (res < 0) {

> > Maybe it needs to handle -EINTR.

> Its behaviour should be retry, right?
> Since these reads are used multiple times in the code, maybe I'm better off
> writing a wrapper function handling also EINTR.

Take a look at readn():

tools/lib/perf/lib.c

static ssize_t ion(bool is_read, int fd, void *buf, size_t n)
{
        void *buf_start = buf;
        size_t left = n;

        while (left) {
                /* buf must be treated as const if !is_read. */
                ssize_t ret = is_read ? read(fd, buf, left) :
                                        write(fd, buf, left);

                if (ret < 0 && errno == EINTR)
                        continue;
                if (ret <= 0)
                        return ret;

                left -= ret;
                buf  += ret;
        }

        BUG_ON((size_t)(buf - buf_start) != n);
        return n;
}

/*
 * Read exactly 'n' bytes or return an error.
 */
ssize_t readn(int fd, void *buf, size_t n)
{
        return ion(true, fd, buf, n);
}
 
 
- Arnaldo