LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Peter Zijlstra <peterz@infradead.org>
To: Song Liu <songliubraving@fb.com>
Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
	acme@kernel.org, mingo@redhat.com, kernel-team@fb.com
Subject: Re: [PATCH bpf-next 1/3] perf: enable branch record for software events
Date: Wed, 25 Aug 2021 14:09:23 +0200	[thread overview]
Message-ID: <YSYy87ta1GpXCCzk@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210824060157.3889139-2-songliubraving@fb.com>

On Mon, Aug 23, 2021 at 11:01:55PM -0700, Song Liu wrote:

>  arch/x86/events/intel/core.c |  5 ++++-
>  arch/x86/events/intel/lbr.c  | 12 ++++++++++++
>  arch/x86/events/perf_event.h |  2 ++
>  include/linux/perf_event.h   | 33 +++++++++++++++++++++++++++++++++
>  kernel/events/core.c         | 28 ++++++++++++++++++++++++++++
>  5 files changed, 79 insertions(+), 1 deletion(-)

No PowerPC support :/

> +void intel_pmu_snapshot_branch_stack(void)
> +{
> +	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
> +
> +	intel_pmu_lbr_disable_all();
> +	intel_pmu_lbr_read();
> +	memcpy(this_cpu_ptr(&perf_branch_snapshot_entries), cpuc->lbr_entries,
> +	       sizeof(struct perf_branch_entry) * x86_pmu.lbr_nr);
> +	*this_cpu_ptr(&perf_branch_snapshot_size) = x86_pmu.lbr_nr;
> +	intel_pmu_lbr_enable_all(false);
> +}

Still has the layering violation and issues vs PMI.

> +#ifdef CONFIG_HAVE_STATIC_CALL
> +DECLARE_STATIC_CALL(perf_snapshot_branch_stack,
> +		    perf_default_snapshot_branch_stack);
> +#else
> +extern void (*perf_snapshot_branch_stack)(void);
> +#endif

That's weird, static call should work unconditionally, and fall back to
a regular function pointer exactly like you do here. Search for:
"Generic Implementation" in include/linux/static_call.h

> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 011cc5069b7ba..b42cc20451709 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c

> +#ifdef CONFIG_HAVE_STATIC_CALL
> +DEFINE_STATIC_CALL(perf_snapshot_branch_stack,
> +		   perf_default_snapshot_branch_stack);
> +#else
> +void (*perf_snapshot_branch_stack)(void) = perf_default_snapshot_branch_stack;
> +#endif

Idem.

Something like:

DEFINE_STATIC_CALL_NULL(perf_snapshot_branch_stack, void (*)(void));

with usage like: static_call_cond(perf_snapshot_branch_stack)();

Should unconditionally work.

> +int perf_read_branch_snapshot(void *buf, size_t len)
> +{
> +	int cnt;
> +
> +	memcpy(buf, *this_cpu_ptr(&perf_branch_snapshot_entries),
> +	       min_t(u32, (u32)len,
> +		     sizeof(struct perf_branch_entry) * MAX_BRANCH_SNAPSHOT));
> +	cnt =  *this_cpu_ptr(&perf_branch_snapshot_size);
> +
> +	return (cnt > 0) ? cnt : -EOPNOTSUPP;
> +}

Doesn't seem used at all..


  reply	other threads:[~2021-08-25 12:10 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-24  6:01 [PATCH bpf-next 0/3] bpf: introduce bpf_get_branch_trace Song Liu
2021-08-24  6:01 ` [PATCH bpf-next 1/3] perf: enable branch record for software events Song Liu
2021-08-25 12:09   ` Peter Zijlstra [this message]
2021-08-25 15:22     ` Song Liu
2021-08-26  7:56       ` kajoljain
2021-08-26 16:41         ` Song Liu
2021-08-24  6:01 ` [PATCH bpf-next 2/3] bpf: introduce helper bpf_get_branch_trace Song Liu
2021-08-25  1:14   ` kernel test robot
2021-08-24  6:01 ` [PATCH bpf-next 3/3] selftests/bpf: add test for bpf_get_branch_trace Song Liu
2021-08-31  1:30 [selftests/bpf] 8dff2c1958: BUG:using_smp_processor_id()in_preemptible kernel test robot
2021-08-31  4:45 ` Song Liu

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=YSYy87ta1GpXCCzk@hirez.programming.kicks-ass.net \
    --to=peterz@infradead.org \
    --cc=acme@kernel.org \
    --cc=bpf@vger.kernel.org \
    --cc=kernel-team@fb.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=songliubraving@fb.com \
    --subject='Re: [PATCH bpf-next 1/3] perf: enable branch record for software events' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).