linux-kernel - Re: [PATCH] kbuild: use -flive-patching when CONFIG

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Date:   Thu, 20 Dec 2018 13:47:53 -0800
From:   Joao Moreira <jmoreira@...e.de>
To:     Miroslav Benes <mbenes@...e.cz>, Jiri Kosina <jikos@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     yamada.masahiro@...ionext.com, michal.lkml@...kovi.net,
        jeyu@...nel.org, pmladek@...e.com, linux-kbuild@...r.kernel.org,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kbuild: use -flive-patching when CONFIG_LIVEPATCH is
 enabled

On 12/20/18 12:33 AM, Miroslav Benes wrote:
> On Wed, 19 Dec 2018, Jiri Kosina wrote:
> 
>> On Wed, 19 Dec 2018, Josh Poimboeuf wrote:
>>
>>> Also the commit message needs an analysis of the performance impacts.
>>
>> Agreed. Especially as it's expected (*) to be completely in the noise
>> particularly for the kernel, it'd be good to have that documented in the
>> changelog.
>>
>> (*) actually measured already for some subset of the IPA optimizations
> 
> Ok, we can do that. I don't expect the results to be different from the
> last measurement as Jiri mentions. The sets of disabled optimizations are
> similar.
> 
> I'll add it to v2.
> 
> On Wed, 19 Dec 2018, Jiri Kosina wrote:
> 
>> On Wed, 19 Dec 2018, Josh Poimboeuf wrote:
>>
>>>>> This option only makes sense for source-based patch generation, so isn't
>>>>> it a bit premature to make this change without proper source-based patch
>>>>> tooling?
>>>>
>>>> The reality is though that before the full-fledged patch tooling exists,
>>>> people are actually already writing livepatches by hand, so this option is
>>>> useful for them.
>>>
>>> Fair enough.
> 
> Yes, that was the reason I sent it. It would not make sense to wait for
> the tooling in this case, because -flive-patching is useful even now,
> since there is a way to prepare livepatches without any tooling.
> 
>>> Though, upstream, almost everybody seems to use kpatch-build, for which
>>> this patch doesn't help.  And people will continue to do so until we
>>> have decent source-based tooling.  Will the klp-convert patches be
>>> revived soon?
>>
>> Let me add Joao, who's working on that.
>>
>> Joao, I think you had something basically ready for upstream exposure,
>> right?
> 
> I think that when Joao posted it a long time ago, the conclusion was that
> it would be better to wait for the source-based tooling and have the
> complete solution. I may misremember though.

Your memories match mine, Miroslav.

FTR, we recently integrated klp-convert to SLE. There were some fixes in 
comparison with the version which was submitted upstream, thus a v2 of 
the patches is necessary.

> 
> If Josh thinks that it would be acceptable to have klp-convert merged even
> without the tooling, I'm all for it.
> 
Of course I can work on that and I'll be glad to do so / submit this new 
version, if this is now something considered useful.

> We're about to start using it at SUSE and staying close to upstream would
> definitely be better.
> 
> Miroslav
>