linux-kernel - Re: [RFC PATCH v1 04/25] printk-rb: add writer interface

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Message-ID: <20190221135140.enamunz6p54dt443@pathway.suse.cz>
Date:   Thu, 21 Feb 2019 14:51:40 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Wang <wonderfly@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Jiri Slaby <jslaby@...e.com>,
        Peter Feiner <pfeiner@...gle.com>,
        linux-serial@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: [RFC PATCH v1 04/25] printk-rb: add writer interface

On Sun 2019-02-17 02:32:22, John Ogness wrote:
> Hi Petr,
> 
> I've made changes to the patch that hopefully align with what you are
> looking for. I would appreciate it if you could go over it and see if
> the changes are in the right direction. And if so, you should decide
> whether I should make these kinds of changes for the whole series and
> submit a v2 before you continue with the review.
> 
> The list of changes:
> 
> - Added comments everywhere I think they could be useful. Is it too
>   much?

Some comments probably can get shortened. But I personally find
them really helpful.

I am not going to do a detailed review of this variant at the moment.
I would like to finish the review of the entire patchset first.

> - I tried moving calc_next() into prb_reserve(), but it was pure
>   insanity. I played with refactoring for a while until I found
>   something that I think looks nice. I moved the implementation of
>   calc_next() along with its containing loop into a new function
>   find_res_ptrs(). This function does what calc_next() and push_tail()
>   did. With this solution, I think prb_reserve() looks pretty
>   clean. However, the optimization of communicating about the wrap is
>   gone. So even though find_res_ptrs() knew if a wrap occurred,
>   prb_reserve() figures it out again for itself. If we want the
>   optimization, I still think the best approach is the -1,0,1 return
>   value of find_res_ptrs().

I still have to go more deeply into it. Anyway, the new code looks
much better than the previous one.

Best Regards,
Petr