linux-kernel - Re: [PATCH 5/7] ramoops: Split ftrace buffer space into per-CPU zones

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Date:   Sun, 9 Oct 2016 10:15:19 -0700
From:   Joel Fernandes <joelaf@...gle.com>
To:     linux-kernel@...r.kernel.org
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joelaf@...gle.com>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Kees Cook <keescook@...omium.org>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH 5/7] ramoops: Split ftrace buffer space into per-CPU zones

On Fri, Oct 7, 2016 at 10:28 PM, Joel Fernandes <joelaf@...gle.com> wrote:
> If FTRACE_PER_CPU flag is passed to ramoops pdata, split the space into
> multiple zones depending on the number of CPUs.
>
> This speeds up the performance of function tracing by about 280% in my tests as
> we avoid the locking. The trade off being lesser space available per CPU.  Let
> the ramoops user decide which option they want based on pdata flag.
>
> Signed-off-by: Joel Fernandes <joelaf@...gle.com>
> ---
>  fs/pstore/ram.c            | 70 +++++++++++++++++++++++++++++++++++-----------
>  include/linux/pstore_ram.h |  3 ++
>  2 files changed, 56 insertions(+), 17 deletions(-)
>
> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
[..]
> @@ -391,14 +418,21 @@ static void ramoops_free_przs(struct ramoops_context *cxt)
>  {
>         int i;
>
> -       if (!cxt->przs)
> -               return;
> +       /* Free dump PRZs */
> +       if (cxt->przs) {
> +               for (i = 0; i < cxt->max_dump_cnt; i++)
> +                       persistent_ram_free(cxt->przs[i]);
>
> -       for (i = 0; i < cxt->max_dump_cnt; i++)
> -               persistent_ram_free(cxt->przs[i]);
> +               kfree(cxt->przs);
> +               cxt->max_dump_cnt = 0;
> +       }
>
> -       kfree(cxt->przs);
> -       cxt->max_dump_cnt = 0;
> +       /* Free ftrace PRZs */
> +       if (cxt->fprzs) {
> +               for (i = 0; i < nr_cpu_ids; i++)
> +                       persistent_ram_free(cxt->przs[i]);

I am supposed to free fprzs[i] here, instead of przs[i]. Also need to
check flag and free correct number of zones. Will fix for v2, sorry
about that.

Thanks,
Joel