linux-kernel - Re: [PATCH] arm64: add architecture specified current_pt

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Message-ID: <CAN1e=SERqTUU_mLwyOQFonz2sVT1xUQAxUs7WOqCNWe_GxCj4w@mail.gmail.com>
Date:	Fri, 19 Feb 2016 20:01:27 +0800
From:	Zhizhou Zhang <zhizhou.zh@...il.com>
To:	Will Deacon <will.deacon@....com>
Cc:	Catalin Marinas <catalin.marinas@....com>, robin.murphy@....com,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: add architecture specified current_pt_regs

On Fri, Feb 19, 2016 at 6:32 PM, Will Deacon <will.deacon@....com> wrote:
> On Fri, Feb 19, 2016 at 10:30:09AM +0800, Zhi-zhou wrote:
>> On Thu, Feb 18, 2016 at 7:58 PM, Catalin Marinas
>> <catalin.marinas@....com> wrote:
>> >
>> > On Thu, Feb 18, 2016 at 07:48:35PM +0800, Zhi-zhou Zhang wrote:
>> > > From: zhizhou <zhizhou.zh@...il.com>
>> > >
>> > > This patch is based on the implementation of arm. The generic
>> > > current_pt_regs is implemented with current->stack. It need to access
>> > > memory that would be too expensive.
>> >
>> > Do you have any performance numbers?
>>
>> I'm using QEMU, so no. Actually this macro isn't heavily used. I just
>> think using the generic
>> implementation is not very nice. It get task_struct from sp_el0, then
>> get stack(which is
>> equal to sp_el0) from task_struct. There are two unnecessary memory accesses.
>
> I'd much rather use the generic implementation unless there's a compelling
> reason not to. "I think it's not very nice" doesn't really cut it for me!
Refer to memory twice may incur cache eviction. I'm really a newbie to
kernel. Anyway, I have a look at kernel and I'm very curious what's
the 'compelling reason' of 16 architectures implement their own
current_pt_regs?
>
> Will



-- 
Regards,
Zhizhou