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SubjectRe: [PATCH] tracing: save cmdline only when task does not exist in savecmd for optimization
On Mon, 11 Oct 2021 19:50:18 +0800
Yang Jihong <yangjihong1@huawei.com> wrote:

> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 7896d30d90f7..a795610a3b37 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2427,8 +2427,11 @@ static int trace_save_cmdline(struct task_struct *tsk)
> savedcmd->cmdline_idx = idx;
> }
>
> - savedcmd->map_cmdline_to_pid[idx] = tsk->pid;
> - set_cmdline(idx, tsk->comm);
> + /* save cmdline only when task does not exist in savecmd */
> + if (savedcmd->map_cmdline_to_pid[idx] != tsk->pid) {
> + savedcmd->map_cmdline_to_pid[idx] = tsk->pid;
> + set_cmdline(idx, tsk->comm);
> + }
>

I now remember why I never did it this way. This breaks saving the command
line when we do an exec.

That is, just because mapped_pid == tsk->pid does not mean that the comm is
the same.

-- Steve

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