linux-kernel - Re: Do we really need curr_target in signal

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Date:	Sat, 1 Feb 2014 00:53:42 +0600
From:	Rakib Mullick <rakib.mullick@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Do we really need curr_target in signal_struct ?

On Thu, Jan 30, 2014 at 1:02 PM, Rakib Mullick <rakib.mullick@...il.com> wrote:
> On Thu, Jan 30, 2014 at 12:32 AM, Oleg Nesterov <oleg@...hat.com> wrote:
>> On 01/29, Rakib Mullick wrote:
>
>>> Are you thinking that , since things are not broken, then we shouldn't
>>> try to do anything?
>>
>> Hmm. No.
>>
>> I am thinking that, since you misunderstood the purpose of ->curr_target,
>> I should probably try to argue with your patch which blindly removes this
>> optimization ?
>>
> Since the optimization (usages of ->curr_target) isn't perfect, so there's
> chance of being misunderstood. This optimization is misleading too (I think),
> cause curr_target don't have anything to do with wants_signal() and
>  ->curr_target is used only for this optimization and to get this optimization
> needs to maintain it properly, and this maintenance does have cost and if
> we don't get benefited too much, then it doesn't worth it (my pov).
>
>> I also think that this logic doesn't look perfect, but this is another
>> story.
>
> Yes, this logic seems need to improve.
>
As you've made few points about the current logic of thread picking in
complete_signal(), I took a look and found that using while_each_thread()
can make things better than current. Although my initial intent of this thread
wasn't related to complete_signal() logic, but as you've pointed out that
things could be better, so I prepared the attached patch (just to address
complete_signal()'s thread finding logic) not using ->curr_target but it's been
kept. What do you think?


Thanks,
Rakib

View attachment "signal_completion.patch" of type "text/x-patch" (1742 bytes)