From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Song Liu <songliubraving@fb.com>
Cc: bpf <bpf@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
kjain@linux.ibm.com, Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH v5 bpf-next 2/3] bpf: introduce helper bpf_get_branch_snapshot
Date: Thu, 2 Sep 2021 18:03:41 -0700 [thread overview]
Message-ID: <CAADnVQKxwUtUJTNjwiU-hmtqjpaTZLXoFzKtK7SME=zLuRbdUg@mail.gmail.com> (raw)
In-Reply-To: <20210902165706.2812867-3-songliubraving@fb.com>
On Thu, Sep 2, 2021 at 9:58 AM Song Liu <songliubraving@fb.com> wrote:
>
> +BPF_CALL_3(bpf_get_branch_snapshot, void *, buf, u32, size, u64, flags)
> +{
> +#ifndef CONFIG_X86
> + return -ENOENT;
> +#else
> + static const u32 br_entry_size = sizeof(struct perf_branch_entry);
> + u32 entry_cnt = size / br_entry_size;
> +
> + if (unlikely(flags))
> + return -EINVAL;
> +
> + if (!buf || (size % br_entry_size != 0))
> + return -EINVAL;
> +
> + entry_cnt = static_call(perf_snapshot_branch_stack)(buf, entry_cnt);
Not taken branches will not be counted even with PERF_SAMPLE_BRANCH_ANY,
right?
Probably the first unlikely(flags) will be a fallthrough in asm.
Maybe worth adding unlikely to 2nd condition as well to make
sure that the compiler will generate default fallthrough code for it ?
So both will not appear in lbr entries?
Or maybe do:
if (unlikely(!buf))
return -EINVAL;
entry_cnt = static_call
if (size % br_entry_size)
return -EINVAL;
The lbr trace will be collected anyway.
If there are jmps in lbr due to earlier "if"s we can move them
after static_call. Like if (unlikely(flags) can be done afterwards too.
Bigger bang for the buck would be static-inline-ing migrate_disable, though.
next prev parent reply other threads:[~2021-09-03 1:03 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-02 16:57 [PATCH v5 bpf-next 0/3] bpf: introduce bpf_get_branch_snapshot Song Liu
2021-09-02 16:57 ` [PATCH v5 bpf-next 1/3] perf: enable branch record for software events Song Liu
2021-09-02 20:49 ` John Fastabend
2021-09-03 8:02 ` Peter Zijlstra
2021-09-03 16:50 ` Song Liu
2021-09-07 18:59 ` Song Liu
2021-09-07 20:50 ` Andrii Nakryiko
2021-09-03 8:27 ` Peter Zijlstra
2021-09-03 16:45 ` Song Liu
2021-09-04 10:18 ` Peter Zijlstra
2021-09-02 16:57 ` [PATCH v5 bpf-next 2/3] bpf: introduce helper bpf_get_branch_snapshot Song Liu
2021-09-02 20:56 ` John Fastabend
2021-09-02 22:04 ` Song Liu
2021-09-02 22:53 ` Andrii Nakryiko
2021-09-02 23:03 ` Song Liu
2021-09-02 23:05 ` Andrii Nakryiko
2021-09-03 1:03 ` Alexei Starovoitov [this message]
2021-09-03 8:28 ` Peter Zijlstra
2021-09-03 16:58 ` Song Liu
2021-09-03 8:47 ` Peter Zijlstra
2021-09-03 17:06 ` Song Liu
2021-09-03 17:10 ` Andrii Nakryiko
2021-09-04 10:24 ` Peter Zijlstra
2021-09-04 10:55 ` Peter Zijlstra
2021-09-02 16:57 ` [PATCH v5 bpf-next 3/3] selftests/bpf: add test for bpf_get_branch_snapshot Song Liu
2021-09-02 21:05 ` John Fastabend
2021-09-02 22:54 ` [PATCH v5 bpf-next 0/3] bpf: introduce bpf_get_branch_snapshot Andrii Nakryiko
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