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 20:40:27 +0200 [thread overview]
Message-ID: <20210910184027.GQ4323@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <96445733-055E-41E3-986B-5E1DC04ADEFA@fb.com>
On Fri, Sep 10, 2021 at 06:27:36PM +0000, Song Liu wrote:
> This works great and saves 3 entries! We have the following now:
Yay!
> ID: 0 from bpf_get_branch_snapshot+18 to intel_pmu_snapshot_branch_stack+0
is unavoidable, we need to end up in intel_pmu_snapshot_branch_stack()
eventually.
> ID: 1 from __brk_limit+477143934 to bpf_get_branch_snapshot+0
could be elided by having the JIT emit the call to
intel_pmu_snapshot_branch_stack directly, instead of laundering it
through that helper I suppose.
> ID: 2 from __brk_limit+477192263 to __brk_limit+477143880 # trampoline
> ID: 3 from __bpf_prog_enter+34 to __brk_limit+477192251
-ENOCLUE
> ID: 4 from migrate_disable+60 to __bpf_prog_enter+9
> ID: 5 from __bpf_prog_enter+4 to migrate_disable+0
I suppose we can reduce that to a single branch if we inline
migrate_disable() here, that thing unfortunately needs one branch
itself.
> ID: 6 from bpf_testmod_loop_test+20 to __bpf_prog_enter+0
And this is the first branch out of the test program, giving 7 entries
now, of which we can remove at least 2 more with a bit of elbow greace,
right?
> ID: 7 from bpf_testmod_loop_test+20 to bpf_testmod_loop_test+13
> ID: 8 from bpf_testmod_loop_test+20 to bpf_testmod_loop_test+13
>
> I will fold this in and send v7.
Excellent.
next prev parent reply other threads:[~2021-09-10 18:40 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 [this message]
2021-09-10 18:50 ` Peter Zijlstra
2021-09-10 19:00 ` Song Liu
2021-09-10 19:08 ` Peter Zijlstra
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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