From: Peter Zijlstra <peterz@infradead.org>
To: Song Liu <songliubraving@fb.com>
Cc: "bpf@vger.kernel.org" <bpf@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"acme@kernel.org" <acme@kernel.org>,
"mingo@redhat.com" <mingo@redhat.com>,
"kjain@linux.ibm.com" <kjain@linux.ibm.com>,
Kernel Team <Kernel-team@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
Andrii Nakryiko <andrii@kernel.org>
Subject: Re: [PATCH v6 bpf-next 1/3] perf: enable branch record for software events
Date: Fri, 10 Sep 2021 21:08:04 +0200 [thread overview]
Message-ID: <20210910190804.GS4323@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <6830FC62-995A-4282-BD30-76E2506ED993@fb.com>
On Fri, Sep 10, 2021 at 07:00:08PM +0000, Song Liu wrote:
> Hmm.. not really. We call migrate_disable() before entering the BPF program.
> And the helper calls snapshot_branch_stack() inside the BPF program. To move
> it to before migrate_disable(), we will have to add a "whether to snapshot
> branch stack" check before entering the BPF program. This check, while is
> cheap, is added to all BPF programs on this hook, even when the program does
> not use snapshot at all. So we would rather keep all logic inside the helper,
> and not touch the common path.
Moo :/ Because I also really don't want to expose struct rq, it's
currently nicely squirelled away in kernel/sched/ and doesn't get
anywhere near include/.
A well, maybe we can do something clever with migrate_disable() itself.
I'll put it on this endless todo list ;-)
next prev parent reply other threads:[~2021-09-10 19:08 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-07 20:27 [PATCH v6 bpf-next 0/3] bpf: introduce bpf_get_branch_snapshot Song Liu
2021-09-07 20:28 ` [PATCH v6 bpf-next 1/3] perf: enable branch record for software events Song Liu
2021-09-10 10:40 ` Peter Zijlstra
2021-09-10 13:54 ` Peter Zijlstra
2021-09-10 18:27 ` Song Liu
2021-09-10 18:40 ` Peter Zijlstra
2021-09-10 18:50 ` Peter Zijlstra
2021-09-10 19:00 ` Song Liu
2021-09-10 19:08 ` Peter Zijlstra [this message]
2021-09-10 19:11 ` Song Liu
2021-09-10 18:51 ` Song Liu
2021-09-07 20:28 ` [PATCH v6 bpf-next 2/3] bpf: introduce helper bpf_get_branch_snapshot Song Liu
2021-09-07 20:28 ` [PATCH v6 bpf-next 3/3] selftests/bpf: add test for bpf_get_branch_snapshot Song Liu
2021-09-07 20:29 ` [PATCH v6 bpf-next 0/3] bpf: introduce bpf_get_branch_snapshot Song Liu
2021-09-07 20:58 ` Andrii Nakryiko
2021-09-09 21:53 ` Song Liu
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