linux-kernel - Re: [PATCH v1] perf record: fix binding of AIO user space buffers to nodes

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Date:   Thu, 12 Mar 2020 14:12:14 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        Jiri Olsa <jolsa@...hat.com>,
        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 v1] perf record: fix binding of AIO user space buffers to
 nodes

Em Thu, Mar 12, 2020 at 07:09:56PM +0300, Alexey Budankov escreveu:
> 
> On 12.03.2020 17:31, Arnaldo Carvalho de Melo wrote:
> > Em Thu, Mar 12, 2020 at 03:21:45PM +0300, Alexey Budankov escreveu:
> >>
> >> Correct maxnode parameter value passed to mbind() syscall to be
> >> the amount of node mask bits to analyze plus 1. Dynamically allocate
> >> node mask memory depending on the index of node of cpu being profiled.
> >> Fixes: c44a8b44ca9f ("perf record: Bind the AIO user space buffers to nodes")
> >> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
> >> ---
> >>  tools/perf/util/mmap.c | 21 +++++++++++++++------
> >>  1 file changed, 15 insertions(+), 6 deletions(-)
> >>
> >> diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
> >> index 3b664fa673a6..6d604cd67a95 100644
> >> --- a/tools/perf/util/mmap.c
> >> +++ b/tools/perf/util/mmap.c
> >> @@ -98,20 +98,29 @@ static int perf_mmap__aio_bind(struct mmap *map, int idx, int cpu, int affinity)
> >>  {
> >>  	void *data;
> >>  	size_t mmap_len;
> >> -	unsigned long node_mask;
> >> +	unsigned long *node_mask;
> >> +	unsigned long node_index;
> >> +	int err = 0;
> >>  
> >>  	if (affinity != PERF_AFFINITY_SYS && cpu__max_node() > 1) {
> >>  		data = map->aio.data[idx];
> >>  		mmap_len = mmap__mmap_len(map);
> >> -		node_mask = 1UL << cpu__get_node(cpu);
> >> -		if (mbind(data, mmap_len, MPOL_BIND, &node_mask, 1, 0)) {
> >> -			pr_err("Failed to bind [%p-%p] AIO buffer to node %d: error %m\n",
> >> -				data, data + mmap_len, cpu__get_node(cpu));
> >> +		node_index = cpu__get_node(cpu);
> >> +		node_mask = bitmap_alloc(node_index + 1);
> >> +		if (!node_mask) {
> >> +			pr_err("Failed to allocate node mask for mbind: error %m\n");
> >>  			return -1;
> >>  		}
> >> +		set_bit(node_index, node_mask);
> >> +		if (mbind(data, mmap_len, MPOL_BIND, node_mask, node_index + 1 + 1/*nr_bits + 1*/, 0)) {
> > 
> >                                                                                   ^^^^^^^^^^^^^^
> > 										  Leftover?
> 
> Intentionally put it here to document kernel behavior for mbind() syscall
> because currently it is different from the man page [1] documented:
> 
> "nodemask points to a bit mask of nodes containing up to maxnode bits.
>  The bit mask size is rounded to the next multiple of sizeof(unsigned
>  long), but the kernel will use bits only up to maxnode.  A NULL value
>  of nodemask or a maxnode value of zero specifies the empty set of
>  nodes.  If the value of maxnode is zero, the nodemask argument is
>  ignored.  Where a nodemask is required, it must contain at least one
>  node that is on-line, allowed by the thread's current cpuset context
>  (unless the MPOL_F_STATIC_NODES mode flag is specified), and contains
>  memory."

Ok, will add the above as a comment above the line with that comment.
 
> ~Alexey
> 
> [1] http://man7.org/linux/man-pages/man2/mbind.2.html

-- 

- Arnaldo