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

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Date:	Wed, 29 Jan 2014 15:55:35 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Rakib Mullick <rakib.mullick@...il.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 01/29, Rakib Mullick wrote:
>
> On Tue, Jan 28, 2014 at 10:43 PM, Oleg Nesterov <oleg@...hat.com> wrote:
>
> > But I guess ->curr_target was added exactly to avoid this loop if
> > possible, assuming that wants_signal(->current_targer) should be
> > likely true. Although perhaps this optimization is too simple.
> >
> Well, this code block will only hit when first check for wants_signal()
> will miss,

Yes,

> that means we need to find some other thread of the group.

Yes,

> 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".

> 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.

Oleg.

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