linux-kernel - RE: [Xen-devel] [PATCH] modify the IO_TLB_SEGSIZE to io_tlb_segsize configurable as flexible requirement about SW-IOMMU.

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Date:	Wed, 11 Feb 2015 08:38:29 +0000
From:	"Wang, Xiaoming" <xiaoming.wang@...el.com>
To:	David Vrabel <david.vrabel@...rix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	"linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
	"pebolle@...cali.nl" <pebolle@...cali.nl>,
	"Zhang, Dongxing" <dongxing.zhang@...el.com>,
	"lauraa@...eaurora.org" <lauraa@...eaurora.org>,
	"d.kasatkin@...sung.com" <d.kasatkin@...sung.com>,
	"heiko.carstens@...ibm.com" <heiko.carstens@...ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ralf@...ux-mips.org" <ralf@...ux-mips.org>,
	"chris@...is-wilson.co.uk" <chris@...is-wilson.co.uk>,
	"takahiro.akashi@...aro.org" <takahiro.akashi@...aro.org>,
	"linux@...izon.com" <linux@...izon.com>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
	"boris.ostrovsky@...cle.com" <boris.ostrovsky@...cle.com>,
	"Liu, Chuansheng" <chuansheng.liu@...el.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: RE: [Xen-devel] [PATCH] modify the IO_TLB_SEGSIZE to io_tlb_segsize
 configurable as flexible requirement about SW-IOMMU.

Dear David

> -----Original Message-----
> From: David Vrabel [mailto:david.vrabel@...rix.com]
> Sent: Tuesday, February 10, 2015 5:46 PM
> To: Wang, Xiaoming; Konrad Rzeszutek Wilk
> Cc: linux-mips@...ux-mips.org; pebolle@...cali.nl; Zhang, Dongxing;
> lauraa@...eaurora.org; d.kasatkin@...sung.com;
> heiko.carstens@...ibm.com; linux-kernel@...r.kernel.org; ralf@...ux-
> mips.org; chris@...is-wilson.co.uk; takahiro.akashi@...aro.org;
> david.vrabel@...rix.com; linux@...izon.com; xen-
> devel@...ts.xenproject.org; boris.ostrovsky@...cle.com; Liu, Chuansheng;
> akpm@...ux-foundation.org
> Subject: Re: [Xen-devel] [PATCH] modify the IO_TLB_SEGSIZE to
> io_tlb_segsize configurable as flexible requirement about SW-IOMMU.
> 
> On 06/02/15 00:10, Wang, Xiaoming wrote:
> >
> >
> >> -----Original Message-----
> >> From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@...cle.com]
> >> Sent: Friday, February 6, 2015 3:33 AM
> >> To: Wang, Xiaoming
> >> Cc: ralf@...ux-mips.org; boris.ostrovsky@...cle.com;
> >> david.vrabel@...rix.com; linux-mips@...ux-mips.org; linux-
> >> kernel@...r.kernel.org; xen-devel@...ts.xenproject.org; akpm@...ux-
> >> foundation.org; linux@...izon.com; lauraa@...eaurora.org;
> >> heiko.carstens@...ibm.com; d.kasatkin@...sung.com;
> >> takahiro.akashi@...aro.org; chris@...is-wilson.co.uk;
> >> pebolle@...cali.nl; Liu, Chuansheng; Zhang, Dongxing
> >> Subject: Re: [PATCH] modify the IO_TLB_SEGSIZE to io_tlb_segsize
> >> configurable as flexible requirement about SW-IOMMU.
> >>
> >> On Fri, Feb 06, 2015 at 07:01:14AM +0800, xiaomin1 wrote:
> >>> The maximum of SW-IOMMU is limited to 2^11*128 = 256K.
> >>> While in different platform and different requirements this seems
> improper.
> >>> So modify the IO_TLB_SEGSIZE to io_tlb_segsize as configurable is
> >>> make
> >> sense.
> >>
> >> More details please. What is the issue you are hitting?
> >>
> > Example:
> > If 1M bytes are requied. There has an error like.
> 
> Instead of allowing the bouncing of such large buffers, could the gadget
> driver be modified to submit the buffers to the hardware in smaller chunks?
> 
> David

Our target is try to make IO_TLB_SEGSIZE configurable.
Neither 256 bytes  or 1M bytes seems suitable value, I think.
It's better to use the tactics something like
kmem_cache_create  in kmalloc function.
But SW-IOMMU seems more lighter.
So we choose variable rather than function.

Xiaoming.
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