From: Peter Zijlstra <peterz@infradead.org>
To: Like Xu <like.xu.linux@gmail.com>
Cc: Song Liu <songliubraving@fb.com>, bpf <bpf@vger.kernel.org>,
Networking <netdev@vger.kernel.org>,
Kernel Team <Kernel-team@fb.com>,
Andrii Nakryiko <andrii@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
like.xu@linux.intel.com
Subject: Re: bpf_get_branch_snapshot on qemu-kvm
Date: Wed, 29 Sep 2021 14:26:07 +0200 [thread overview]
Message-ID: <YVRbX6vBgz+wYzZK@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <d75f6a9a-dbb3-c725-c001-ec9bdd55173f@gmail.com>
On Wed, Sep 29, 2021 at 08:05:24PM +0800, Like Xu wrote:
> On 29/9/2021 3:35 pm, Peter Zijlstra wrote:
> > > [ 139.494159] unchecked MSR access error: WRMSR to 0x3f1 (tried to write 0x0000000000000000) at rIP: 0xffffffff81011a8b (intel_pmu_snapshot_branch_stack+0x3b/0xd0)
>
> Uh, it uses a PEBS counter to sample or count, which is not yet upstream but
> should be soon.
Ooh that's PEBS_ENABLE
> Song, can you try to fix bpf_get_branch_snapshot on a normal PMC counter,
> or where is the src for bpf_get_branch_snapshot? I am more than happy to help.
Nah, all that code wants to do is disable PEBS... and virt being virt,
it's all sorts of weird with f/m/s :/
I so hate all that. So there's two solutions:
- get confirmation that clearing GLOBAL_CTRL is suffient to supress
PEBS, in which case we can simply remove the PEBS_ENABLE clear.
or
- create another 2 intel_pmu_snapshot_{,arch_}branch_stack() copies
that omit the PEBS thing.
next prev parent reply other threads:[~2021-09-29 12:26 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-29 0:04 bpf_get_branch_snapshot on qemu-kvm Song Liu
2021-09-29 7:35 ` Peter Zijlstra
2021-09-29 12:05 ` Like Xu
2021-09-29 12:26 ` Peter Zijlstra [this message]
2021-09-29 14:42 ` Song Liu
2021-09-29 15:59 ` Peter Zijlstra
2021-09-29 16:35 ` Liang, Kan
2021-09-29 20:05 ` Song Liu
2021-10-08 3:34 ` Like Xu
2021-10-08 5:46 ` Song Liu
2021-10-08 6:36 ` Like Xu
2021-10-08 17:08 ` Song Liu
2021-10-09 9:03 ` Like Xu
2021-10-26 7:09 ` Song Liu
2021-10-28 3:09 ` Like Xu
2021-10-29 18:09 ` Song Liu
2021-09-29 23:20 ` Andi Kleen
2021-09-29 14:39 ` Song Liu
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