linux-kernel - Re: [RFC PATCH v3 5/7] powerpc: 'current_set' is now a table of task

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Date:   Wed, 3 Oct 2018 16:09:11 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Christophe LEROY <christophe.leroy@....fr>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        aneesh.kumar@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RFC PATCH v3 5/7] powerpc: 'current_set' is now a table of
 task_struct pointers

On Wed, 3 Oct 2018 08:00:43 +0200
Christophe LEROY <christophe.leroy@....fr> wrote:

> Le 03/10/2018 à 07:41, Nicholas Piggin a écrit :
> > On Mon,  1 Oct 2018 12:30:27 +0000 (UTC)
> > Christophe Leroy <christophe.leroy@....fr> wrote:
> >   
> >> The table of pointers 'current_set' has been used for retrieving
> >> the stack and current. They used to be thread_info pointers as
> >> they were pointing to the stack and current was taken from the
> >> 'task' field of the thread_info.
> >>
> >> Now, the pointers of 'current_set' table are now both pointers
> >> to task_struct and pointers to thread_info.
> >>
> >> As they are used to get current, and the stack pointer is
> >> retrieved from current's stack field, this patch changes
> >> their type to task_struct, and renames secondary_ti to
> >> secondary_current.  
> > 
> > I'm not sure if current_set is actually needed is it? Because
> > 64-bit already initializes paca->ksave / PACAKSAVE. That might
> > be a cleanup to do after your series.  
> 
> head_64.S contains:
> 
> __secondary_start:
> 	/* Set thread priority to MEDIUM */
> 	HMT_MEDIUM
> 
> 	/* Initialize the kernel stack */
> 	LOAD_REG_ADDR(r3, current_set)
> 	sldi	r28,r24,3		/* get current_set[cpu#]	 */
> 	ldx	r14,r3,r28
> 	addi	r14,r14,THREAD_SIZE-STACK_FRAME_OVERHEAD
> 	std	r14,PACAKSAVE(r13)

Right, I don't *think* that's needed because boot CPU should already
have set PACAKSAVE before starting secondaries here. ld r14,PACAKSAVE
should have the same result I think.

But never mind that for your series, just something I saw that could
be cleaned up.

Thanks,
Nick