linux-kernel - Re: [PATCH v2] printk: ringbuffer: Improve prb_next

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Date:   Thu, 7 Apr 2022 17:44:31 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     pmladek@...e.com
Cc:     Chunlei.wang@...iatek.com, john.ogness@...utronix.de,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>, senozhatsky@...omium.org,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH v2] printk: ringbuffer: Improve prb_next_seq() performance

Messed up mail headers. I'll resend this with proper mail headers.

-Saravana

On Thu, Apr 7, 2022 at 5:36 PM Saravana Kannan <saravanak@...gle.com> wrote:
>
> > --- a/kernel/printk/printk_ringbuffer.h
> > +++ b/kernel/printk/printk_ringbuffer.h
> > @@ -75,6 +75,7 @@ struct prb_desc_ring {
> >  struct printk_info *infos;
> >  atomic_long_t head_id;
> >  atomic_long_t tail_id;
> > + atomic_long_t last_finalized_id;
>
> I really know nothing about this code, but while looking around
> kernel/printk/ I noticed kernel/printk/printk.c has these lines in
> log_buf_vmcoreinfo_setup().
>
>         VMCOREINFO_STRUCT_SIZE(prb_desc_ring);
>         VMCOREINFO_OFFSET(prb_desc_ring, count_bits);
>         VMCOREINFO_OFFSET(prb_desc_ring, descs);
>         VMCOREINFO_OFFSET(prb_desc_ring, infos);
>         VMCOREINFO_OFFSET(prb_desc_ring, head_id);
>         VMCOREINFO_OFFSET(prb_desc_ring, tail_id);
>
> Would this header file change also require a change to that location?
> Something like
>
>         VMCOREINFO_OFFSET(prb_desc_ring, head_id);
>         VMCOREINFO_OFFSET(prb_desc_ring, tail_id);
> +        VMCOREINFO_OFFSET(prb_desc_ring, last_finalized_id);
>
> -Saravana
>
> > };
> >
> > /*
> > @@ -258,6 +259,7 @@ static struct printk_ringbuffer name = { \
> >  .infos = &_##name##_infos[0], \
> >  .head_id = ATOMIC_INIT(DESC0_ID(descbits)), \
> >  .tail_id = ATOMIC_INIT(DESC0_ID(descbits)), \
> > + .last_finalized_id = ATOMIC_INIT(DESC0_ID(descbits)), \
> >  }, \
> >  .text_data_ring = { \
> >  .size_bits = (avgtextbits) + (descbits), \