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

Wang, Xiaoming
2015-02-11T08:40:08Z

Dear David

> -----Original Message-----
> From: David Vrabel [mailto:david.vrabel@citrix.com]
> Sent: Tuesday, February 10, 2015 5:46 PM
> To: Wang, Xiaoming; Konrad Rzeszutek Wilk
> Cc: linux-mips@linux-mips.org; pebolle@tiscali.nl; Zhang, Dongxing;
> lauraa@codeaurora.org; d.kasatkin@samsung.com;
> heiko.carstens@de.ibm.com; linux-kernel@vger.kernel.org; ralf@linux-
> mips.org; chris@chris-wilson.co.uk; takahiro.akashi@linaro.org;
> david.vrabel@citrix.com; linux@horizon.com; xen-
> devel@lists.xenproject.org; boris.ostrovsky@oracle.com; Liu, Chuansheng;
> akpm@linux-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@oracle.com]
> >> Sent: Friday, February 6, 2015 3:33 AM
> >> To: Wang, Xiaoming
> >> Cc: ralf@linux-mips.org; boris.ostrovsky@oracle.com;
> >> david.vrabel@citrix.com; linux-mips@linux-mips.org; linux-
> >> kernel@vger.kernel.org; xen-devel@lists.xenproject.org; akpm@linux-
> >> foundation.org; linux@horizon.com; lauraa@codeaurora.org;
> >> heiko.carstens@de.ibm.com; d.kasatkin@samsung.com;
> >> takahiro.akashi@linaro.org; chris@chris-wilson.co.uk;
> >> pebolle@tiscali.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.