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Subject: Re: [PATCH] x86: fix get_wchan() not support the ORC unwinder
To:     Qi Zheng <zhengqi.arch@bytedance.com>, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, hpa@zytor.com,
        peterz@infradead.org, x86@kernel.org
Cc:     linux-kernel@vger.kernel.org, songmuchun@bytedance.com
References: <20210611124642.72910-1-zhengqi.arch@bytedance.com>
From:   Andy Lutomirski <luto@kernel.org>
Message-ID: <06292162-5a44-6f91-140d-e1211c006ad0@kernel.org>
Date:   Mon, 14 Jun 2021 09:21:12 -0700
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On 6/11/21 5:46 AM, Qi Zheng wrote:
> Currently, the kernel CONFIG_UNWINDER_ORC option is enabled by
> default on x86, but the implementation of get_wchan() is still
> based on the frame pointer unwinder, so the /proc/<pid>/wchan
> always return 0 regardless of whether the task <pid> is running.
> 
> We reimplement the get_wchan() by calling stack_trace_save_tsk(),
> which is adapted to the ORC and frame pointer unwinders.

How much slower does this make ps?

--Andy