linux-kernel - RE: [PATCH v10 3/5] CPM/QE: use genalloc to manage CPM/QE muram

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Date:	Wed, 23 Sep 2015 05:28:46 +0000
From:	Zhao Qiang <qiang.zhao@...escale.com>
To:	Scott Wood <scottwood@...escale.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"lauraa@...eaurora.org" <lauraa@...eaurora.org>,
	Xiaobo Xie <X.Xie@...escale.com>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
	Li Leo <LeoLi@...escale.com>,
	"paulus@...ba.org" <paulus@...ba.org>
Subject: RE: [PATCH v10 3/5] CPM/QE: use genalloc to manage CPM/QE muram

On Wen, Sep 23, 2015 at 12:03 AM +0800, Wood Scott-B07421 wrote:

> -----Original Message-----
> From: Wood Scott-B07421
> Sent: Wednesday, September 23, 2015 12:03 PM
> To: Zhao Qiang-B45475
> Cc: linux-kernel@...r.kernel.org; linuxppc-dev@...ts.ozlabs.org;
> lauraa@...eaurora.org; Xie Xiaobo-R63061; benh@...nel.crashing.org; Li
> Yang-Leo-R58472; paulus@...ba.org
> Subject: Re: [PATCH v10 3/5] CPM/QE: use genalloc to manage CPM/QE muram
> 
> On Tue, 2015-09-22 at 21:20 -0500, Zhao Qiang-B45475 wrote:
> > On Wen, Sep 23, 2015 at 8:19 AM +0800, Wood Scott-B07421 wrote:
> >
> > > > > >  {
> > > > > > - int ret;
> > > > > > +
> > > > > > + unsigned long start;
> > > > > >   unsigned long flags;
> > > > > > + unsigned long size_alloc = size; struct muram_block *entry;
> > > > > > + int end_bit; int order = muram_pool->min_alloc_order;
> > > > > >
> > > > > >   spin_lock_irqsave(&cpm_muram_lock, flags);
> > > > > > - ret = rh_free(&cpm_muram_info, offset);
> > > > > > + end_bit = (offset >> order) + ((size + (1UL << order) - 1)
> > > > > > + >>
> > > > > order);
> > > > > > + if ((offset + size) > (end_bit << order))
> > > > > > +         size_alloc = size + (1UL << order);
> > > > >
> > > > > Why do you need to do all these calculations here?
> > > >
> > > > So do it in gen_pool_fixed_alloc?
> > >
> > > Could you explain why they're needed at all?
> >
> > Why it does the calculations?
> > If the min block of gen_pool is 8 bytes, and I want to allocate a
> > Region with offset=7, size=8bytes, I actually need block 0 and block
> > 1, And the allocation will give me block 0.
> 
> How can you have offset 7 if the minimum order is 2 bytes?

Offset has no relationship with minimum order, it is not decided by minimum order.
I want to allocate a specific region with offset=7, then algo to calculate the block bit.
And I just take it for example, it is not I really need to region offset=7.

So, now minimum order is 2 bytes. If offset=7, size=4bytes needed, it actually allocate 6-12 to me.
so I need to check if it is necessary to plus a block(2bytes) to size before allocation.  

-Zhao