* [PATCH] libbpf: Use sysconf to simplify libbpf_num_possible_cpus
@ 2021-09-21 6:04 Muhammad Falak R Wani
2021-09-21 23:20 ` Andrii Nakryiko
0 siblings, 1 reply; 3+ messages in thread
From: Muhammad Falak R Wani @ 2021-09-21 6:04 UTC (permalink / raw)
To: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko
Cc: Martin KaFai Lau, Song Liu, Yonghong Song, John Fastabend,
KP Singh, netdev, bpf, linux-kernel, Muhammad Falak R Wani
Simplify libbpf_num_possible_cpus by using sysconf(_SC_NPROCESSORS_CONF)
instead of parsing a file.
This patch is a part of libbpf-1.0 milestone.
Reference: https://github.com/libbpf/libbpf/issue/383
Signed-off-by: Muhammad Falak R Wani <falakreyaz@gmail.com>
---
tools/lib/bpf/libbpf.c | 16 +++-------------
1 file changed, 3 insertions(+), 13 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index da65a1666a5e..1d730b08ee44 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -10765,25 +10765,15 @@ int parse_cpu_mask_file(const char *fcpu, bool **mask, int *mask_sz)
int libbpf_num_possible_cpus(void)
{
- static const char *fcpu = "/sys/devices/system/cpu/possible";
static int cpus;
- int err, n, i, tmp_cpus;
- bool *mask;
+ int tmp_cpus;
tmp_cpus = READ_ONCE(cpus);
if (tmp_cpus > 0)
return tmp_cpus;
- err = parse_cpu_mask_file(fcpu, &mask, &n);
- if (err)
- return libbpf_err(err);
-
- tmp_cpus = 0;
- for (i = 0; i < n; i++) {
- if (mask[i])
- tmp_cpus++;
- }
- free(mask);
+ tmp_cpus = sysconf(_SC_NPROCESSORS_CONF);
+ /* sysconf sets errno; no need to use libbpf_err */
WRITE_ONCE(cpus, tmp_cpus);
return tmp_cpus;
--
2.17.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] libbpf: Use sysconf to simplify libbpf_num_possible_cpus
2021-09-21 6:04 [PATCH] libbpf: Use sysconf to simplify libbpf_num_possible_cpus Muhammad Falak R Wani
@ 2021-09-21 23:20 ` Andrii Nakryiko
2021-09-22 3:21 ` Muhammad Falak Wani
0 siblings, 1 reply; 3+ messages in thread
From: Andrii Nakryiko @ 2021-09-21 23:20 UTC (permalink / raw)
To: Muhammad Falak R Wani
Cc: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko,
Martin KaFai Lau, Song Liu, Yonghong Song, John Fastabend,
KP Singh, Networking, bpf, open list
On Mon, Sep 20, 2021 at 11:04 PM Muhammad Falak R Wani
<falakreyaz@gmail.com> wrote:
>
> Simplify libbpf_num_possible_cpus by using sysconf(_SC_NPROCESSORS_CONF)
> instead of parsing a file.
> This patch is a part of libbpf-1.0 milestone.
>
> Reference: https://github.com/libbpf/libbpf/issue/383
I've been asking people to use a reference style like this, so that we
don't confuse this with proper Linux tags. It's also useful to use
"Closes: " keyword to let Github auto-close the issue when this patch
eventually is synced into Github. So in this case I'd phrase
everything as:
"This patch is a part ([0]) of libbpf-1.0 milestone.
[0] Closes: https://github.com/libbpf/libbpf/issue/383
Please update in the next revision.
Also, keep in mind that we ask to use "[PATCH bpf-next]" prefix when
submitting patches against the bpf-next kernel tree. It makes the
intent clear and our BPF CI system knows which tree to test against.
Thanks.
>
> Signed-off-by: Muhammad Falak R Wani <falakreyaz@gmail.com>
> ---
> tools/lib/bpf/libbpf.c | 16 +++-------------
> 1 file changed, 3 insertions(+), 13 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index da65a1666a5e..1d730b08ee44 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -10765,25 +10765,15 @@ int parse_cpu_mask_file(const char *fcpu, bool **mask, int *mask_sz)
>
> int libbpf_num_possible_cpus(void)
> {
> - static const char *fcpu = "/sys/devices/system/cpu/possible";
> static int cpus;
> - int err, n, i, tmp_cpus;
> - bool *mask;
> + int tmp_cpus;
>
> tmp_cpus = READ_ONCE(cpus);
> if (tmp_cpus > 0)
> return tmp_cpus;
>
> - err = parse_cpu_mask_file(fcpu, &mask, &n);
> - if (err)
> - return libbpf_err(err);
> -
> - tmp_cpus = 0;
> - for (i = 0; i < n; i++) {
> - if (mask[i])
> - tmp_cpus++;
> - }
> - free(mask);
> + tmp_cpus = sysconf(_SC_NPROCESSORS_CONF);
> + /* sysconf sets errno; no need to use libbpf_err */
I'd say it's still a good idea for explicitness and to show that we
didn't forget about it :) Plus, if it actually ever fails, we don't
want to WRITE_ONCE() here, so please follow the same error handling
logic as it was previously with parse_cpu_mask_file.
>
> WRITE_ONCE(cpus, tmp_cpus);
> return tmp_cpus;
> --
> 2.17.1
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] libbpf: Use sysconf to simplify libbpf_num_possible_cpus
2021-09-21 23:20 ` Andrii Nakryiko
@ 2021-09-22 3:21 ` Muhammad Falak Wani
0 siblings, 0 replies; 3+ messages in thread
From: Muhammad Falak Wani @ 2021-09-22 3:21 UTC (permalink / raw)
To: Andrii Nakryiko
Cc: Muhammad Falak R Wani, Alexei Starovoitov, Daniel Borkmann,
Andrii Nakryiko, Martin KaFai Lau, Song Liu, Yonghong Song,
John Fastabend, KP Singh, Networking, bpf, open list
> "This patch is a part ([0]) of libbpf-1.0 milestone.
>
> [0] Closes: https://github.com/libbpf/libbpf/issue/383
>
> Please update in the next revision.
Sure, will send in a V2 of the patch.
>
>
> Also, keep in mind that we ask to use "[PATCH bpf-next]" prefix when
> submitting patches against the bpf-next kernel tree. It makes the
> intent clear and our BPF CI system knows which tree to test against.
> Thanks.
>
Apologies, duly noted for subsequent patches.
> I'd say it's still a good idea for explicitness and to show that we
> didn't forget about it :) Plus, if it actually ever fails, we don't
> want to WRITE_ONCE() here, so please follow the same error handling
> logic as it was previously with parse_cpu_mask_file.
>
> >
> > WRITE_ONCE(cpus, tmp_cpus);
> > return tmp_cpus;
Sure, will adhere to the coding style.
Thank you for your reivew.
-mfrw
^ permalink raw reply [flat|nested] 3+ messages in thread
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2021-09-21 6:04 [PATCH] libbpf: Use sysconf to simplify libbpf_num_possible_cpus Muhammad Falak R Wani
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2021-09-22 3:21 ` Muhammad Falak Wani
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