linux-kernel - Re: [PATCH v7 01/13] tools/libperf: introduce notion of static polled file descriptors

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Message-ID: <3442cc55-d189-b349-28e4-db3367f1b23a@linux.intel.com>
Date:   Mon, 15 Jun 2020 20:38:04 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 01/13] tools/libperf: introduce notion of static polled
 file descriptors


On 09.06.2020 17:56, Jiri Olsa wrote:
> On Mon, Jun 08, 2020 at 08:18:20PM +0300, Alexey Budankov wrote:
> 
> SNIP
> 

<SNIP>

> 
> another idea is to forbid filter to screw the array
> and return only remaining number, like below
> 
> jirka
> 
> 
> ---
> diff --git a/tools/lib/api/fd/array.c b/tools/lib/api/fd/array.c
> index 58d44d5eee31..89f9a2193c2d 100644
> --- a/tools/lib/api/fd/array.c
> +++ b/tools/lib/api/fd/array.c
> @@ -93,22 +93,21 @@ int fdarray__filter(struct fdarray *fda, short revents,
>  		return 0;
>  
>  	for (fd = 0; fd < fda->nr; ++fd) {
> +		if (!fda->entries[fd].events)

If we change it to
		if (!fda->entries[fd].revents)
and fix indices returned by fdarray__add() between fdarray__filter() then
it is possible to check fds status by the pos and process and zero its
revents prior fdarray__filter(). In this case fdarray__filter() would count
the number of fds skipping the ones with zeroed revents.
 
Looks like it solves current task avoiding explicit fds typing and even
providing some more flexibility for other fds different from event and ctl
ones. I will try to come up with a version implementing this approach.

~Alexey

> +			continue;
> +
>  		if (fda->entries[fd].revents & revents) {
>  			if (entry_destructor)
>  				entry_destructor(fda, fd, arg);
>  
> +			fda->entries[fd].revents = fda->entries[fd].events = 0;
>  			continue;
>  		}
>  
> -		if (fd != nr) {
> -			fda->entries[nr] = fda->entries[fd];
> -			fda->priv[nr]	 = fda->priv[fd];
> -		}
> -
>  		++nr;
>  	}
>  
> -	return fda->nr = nr;
> +	return nr;
>  }
>  
>  int fdarray__poll(struct fdarray *fda, int timeout)
> diff --git a/tools/perf/tests/fdarray.c b/tools/perf/tests/fdarray.c
> index c7c81c4a5b2b..d0c8a05aab2f 100644
> --- a/tools/perf/tests/fdarray.c
> +++ b/tools/perf/tests/fdarray.c
> @@ -12,6 +12,7 @@ static void fdarray__init_revents(struct fdarray *fda, short revents)
>  
>  	for (fd = 0; fd < fda->nr; ++fd) {
>  		fda->entries[fd].fd	 = fda->nr - fd;
> +		fda->entries[fd].events  = revents;
>  		fda->entries[fd].revents = revents;
>  	}
>  }
> @@ -29,7 +30,7 @@ static int fdarray__fprintf_prefix(struct fdarray *fda, const char *prefix, FILE
>  
>  int test__fdarray__filter(struct test *test __maybe_unused, int subtest __maybe_unused)
>  {
> -	int nr_fds, expected_fd[2], fd, err = TEST_FAIL;
> +	int nr_fds, err = TEST_FAIL;
>  	struct fdarray *fda = fdarray__new(5, 5);
>  
>  	if (fda == NULL) {
> @@ -55,7 +56,6 @@ int test__fdarray__filter(struct test *test __maybe_unused, int subtest __maybe_
>  
>  	fdarray__init_revents(fda, POLLHUP);
>  	fda->entries[2].revents = POLLIN;
> -	expected_fd[0] = fda->entries[2].fd;
>  
>  	pr_debug("\nfiltering all but fda->entries[2]:");
>  	fdarray__fprintf_prefix(fda, "before", stderr);
> @@ -66,17 +66,9 @@ int test__fdarray__filter(struct test *test __maybe_unused, int subtest __maybe_
>  		goto out_delete;
>  	}
>  
> -	if (fda->entries[0].fd != expected_fd[0]) {
> -		pr_debug("\nfda->entries[0].fd=%d != %d\n",
> -			 fda->entries[0].fd, expected_fd[0]);
> -		goto out_delete;
> -	}
> -
>  	fdarray__init_revents(fda, POLLHUP);
>  	fda->entries[0].revents = POLLIN;
> -	expected_fd[0] = fda->entries[0].fd;
>  	fda->entries[3].revents = POLLIN;
> -	expected_fd[1] = fda->entries[3].fd;
>  
>  	pr_debug("\nfiltering all but (fda->entries[0], fda->entries[3]):");
>  	fdarray__fprintf_prefix(fda, "before", stderr);
> @@ -88,14 +80,6 @@ int test__fdarray__filter(struct test *test __maybe_unused, int subtest __maybe_
>  		goto out_delete;
>  	}
>  
> -	for (fd = 0; fd < 2; ++fd) {
> -		if (fda->entries[fd].fd != expected_fd[fd]) {
> -			pr_debug("\nfda->entries[%d].fd=%d != %d\n", fd,
> -				 fda->entries[fd].fd, expected_fd[fd]);
> -			goto out_delete;
> -		}
> -	}
> -
>  	pr_debug("\n");
>  
>  	err = 0;
>