linux-kernel - Re: [PATCH] sched: make struct task

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Message-ID: <20190903181920.GA22358@avx2>
Date:   Tue, 3 Sep 2019 21:19:20 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     mingo@...hat.com, peterz@...radead.org,
        linux-kernel@...r.kernel.org, rcu@...r.kernel.org,
        linux-block@...r.kernel.org, dm-devel@...hat.com, axboe@...nel.dk,
        aarcange@...hat.com
Subject: Re: [PATCH] sched: make struct task_struct::state 32-bit

On Tue, Sep 03, 2019 at 06:29:06PM +0100, Valentin Schneider wrote:
> On 02/09/2019 22:05, Alexey Dobriyan wrote:
> > 32-bit accesses are shorter than 64-bit accesses on x86_64.
> > Nothing uses 64-bitness of ->state.

> It looks like you missed a few places. There's a long prev_state in
> sched/core.c::finish_task_switch() for instance.
> 
> I suppose that's where coccinelle oughta help but I'm really not fluent
> in that. Is there a way to make it match p.state accesses with p task_struct?
> And if so, can we make it change the type of the variable being read from
> / written to?

Coccinelle is interesting: basic

	- foo
	+ bar

doesn't find "foo" in function arguments.

I'm scared of coccinelle.

> How did you come up with this changeset, did you pickaxe for some regexp?

No, manually, backtracking up to the call chain.
Maybe I missed a few places.