Hello Pratyush,
>On Monday 24 October 2016 10:18 PM, Pratyush Anand wrote:
>> page_offset can always be calculated as 'virtual - physical' for a direct
>> mapping area on x86. Therefore, remove the version dependent calculation
>> and use this method.
>>
>> Signed-off-by: Pratyush Anand <panand at redhat.com>
>> ---
>> arch/x86_64.c | 24 ++++++++++++++++++++----
>> 1 file changed, 20 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86_64.c b/arch/x86_64.c
>> index ddf7be6bc57b..a96fd8ae00a1 100644
>> --- a/arch/x86_64.c
>> +++ b/arch/x86_64.c
>> @@ -44,6 +44,24 @@ get_xen_p2m_mfn(void)
>> return NOT_FOUND_LONG_VALUE;
>> }
>>
>> +static int
>> +get_page_offset_x86_64(void)
>> +{
>> + int i;
>> + unsigned long long phys_start;
>> + unsigned long long virt_start;
>> +
>> + for (i = 0; get_pt_load(i, &phys_start, NULL, &virt_start, NULL); i++) {
>> + if (virt_start >= __START_KERNEL_map) {
>
>OK..So, this is the problem. We should have
>
>if (virt_start < __START_KERNEL_map) {
>
>Kernel text region lies above __START_KERNEL_map, which is linearly
>mapped however not a direct mapping. Direct mapping region lies below it
>instead. So, page_offset can only be calculated with a region which is
>below __START_KERNEL_map.
>
>Thanks Baoquan for finding it.
Could you explain the issue in more detail, what is the difference
between "linear map" and "direct map" ?
BTW, I confirmed that the difference of v2 patch is only this and
the result of benchmark looks great, thank you very much.
Regards,
Atsushi Kumagai
>> + info->page_offset = virt_start - phys_start;
>> + return TRUE;
>> + }
>> + }
>> +
>> + ERRMSG("Can't get any pt_load to calculate page offset.\n");
>> + return FALSE;
>> +}
>> +
>> int
>> get_phys_base_x86_64(void)
>> {
>> @@ -159,10 +177,8 @@ get_versiondep_info_x86_64(void)
>> else
>> info->max_physmem_bits = _MAX_PHYSMEM_BITS_2_6_31;
>>
>> - if (info->kernel_version < KERNEL_VERSION(2, 6, 27))
>> - info->page_offset = __PAGE_OFFSET_ORIG;
>> - else
>> - info->page_offset = __PAGE_OFFSET_2_6_27;
>> + if (!get_page_offset_x86_64())
>> + return FALSE;
>>
>> if (info->kernel_version < KERNEL_VERSION(2, 6, 31)) {
>> info->vmalloc_start = VMALLOC_START_ORIG;
>>
>
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