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

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Message-ID: <CADZ9YHjEfEWJx5z_5KZnfQAVHXY3u613XV7vdZqjts4zFR3_=g@mail.gmail.com>
Date:	Wed, 29 Jan 2014 22:07:22 +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 Wed, Jan 29, 2014 at 8:55 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> On 01/29, Rakib Mullick wrote:
>>
>> On Tue, Jan 28, 2014 at 10:43 PM, Oleg Nesterov <oleg@...hat.com> wrote:
>>
>
>> AFAIU, ->current_target is only a loop breaker to avoid infinite loop,
>
> No. It caches the last result of "find a thread which can handle this
> group-wide signal".
>
The reason behind of my understanding is the following comments:

                                /*
                                 * No thread needs to be woken.
                                 * Any eligible threads will see
                                 * the signal in the queue soon.
                                 */

What if, there's no thread in a group wants_signal()? Or it can't
practically happen?

>> but - by using while_each_thread() we can remove it completely, thus
>> helps to get rid from maintaining it too.
>
> ... and remove the optimization above.
>
>> I'll prepare a proper patch with you suggestions for reviewing.
>
> I am not sure we want this patch. Once again, I do not know how much
> ->curr_target helps, and certainaly it can't help always. But you
> should not blindly remove it just because yes, sure, it is not strictly
> needed to find a wants_signal() thread.
>
Are you thinking that , since things are not broken, then we shouldn't
try to do anything?

Thanks,
Rakib
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