Remove muli at il.ibm.com from CC, this email isn't valid now.
On 02/19/14 at 09:36pm, Vivek Goyal wrote:
> On Wed, Feb 19, 2014 at 05:04:22PM -0700, Jon Mason wrote:
> > On Tue, Feb 18, 2014 at 11:18 PM, WANG Chao <chaowang at redhat.com> wrote:
> > > Hi, All
> > >
> > > arch/x86/kernel/pci-calgary.c is the only user of saved_max_pfn today:
> > >
> > > int __init detect_calgary(void)
> > > {
> > > [..]
> > > specified_table_size = determine_tce_table_size((is_kdump_kernel() ?
> > > saved_max_pfn : max_pfn) * PAGE_SIZE);
> > > [..]
> > > }
> >
> > IIUC, the purpose of this code is to reuse the TCE table from the
> > previous kernel. Thus, it needs to be of the same size as the
> > pre-kdump kernel. It is using the max_pfn to determine the TCE table
> > size in the non-kdump case. If there is another way to determine the
> > size it used before, then I am fine making the change to use that way.
>
> How about passing old tce table size on command line to second kernel.
> Given the fact that it is specific to calgary only, we can it very
> specific. Say calgary_iommu_old_tce_table_sz=<size>.
Don't need to introduce a new parameter, this is already there:
calgary=[64k,128k,256k,512k,1M,2M,4M,8M]
>
> But we will then need to know the size of TCE table in first kernel. Is
> this information exported to user space somewhere?
If this value isn't exported to userspace or even won't in the future, I think
the table size also can be determined by userspace. We can implement something like the
kernel does in kexec.
The calgary code:
static inline int __init determine_tce_table_size(u64 ram)
{
int ret;
if (specified_table_size != TCE_TABLE_SIZE_UNSPECIFIED)
return specified_table_size;
/*
* Table sizes are from 0 to 7 (TCE_TABLE_SIZE_64K to
* TCE_TABLE_SIZE_8M). Table size 0 has 8K entries and each
* larger table size has twice as many entries, so shift the
* max ram address by 13 to divide by 8K and then look at the
* order of the result to choose between 0-7.
*/
ret = get_order(ram >> 13);
if (ret > TCE_TABLE_SIZE_8M)
ret = TCE_TABLE_SIZE_8M;
return ret;
}
But it still no clear to me how I can determine calgary iommu is in use in 1st kernel.
Thanks
WANG Chao
