On Fri, Oct 27, 2017 at 10:57:13AM +0530, Aneesh Kumar K.V wrote:
>
>
> On 10/27/2017 10:04 AM, Paul Mackerras wrote:
> >On Fri, Oct 27, 2017 at 09:38:17AM +0530, Aneesh Kumar K.V wrote:
> >>Hi,
> >>
> >>With hash translation mode we always tracked the hash pte slot details in
> >>linux page table.
> >>This occupied space in the linux page table and also limitted our ability
> >>to support
> >>linux features that require additional PTE bits. This series attempt to
> >>lift this
> >>limitation by not tracking slot number in linux page table. We still track
> >>slot details
> >>w.r.t Transparent Hugepage entries because an invalidate there requires us
> >>to go through
> >>all the 256 hash pte slots. So tracking whether hash page table entry is
> >>valid helps us in
> >>avoiding a lot of hcalls there. With THP entries we don't keep slot details
> >>in the primary
> >>linux page table entry but in the second half of page table. Hence tracking
> >>slot details
> >>for THP doesn't take up space in PTE.
> >>
> >>Even though we don't track slot, for removing/updating hash page table
> >>entry, PAPR hcalls expect
> >>hash page table slot details. On pseries we find slot using H_READ hcall
> >>using H_READ_4 flags.
> >>This implies an additional 2 hcalls in the updatepp and remove paths. The
> >>patch series also
> >>attempt to limit the impact of this by adding new hcalls that does
> >>remove/update of hash page table
> >>entry using hash value instead of hash page table slot.
> >>
> >>Below is the performance numbers observed when running a workload that does
> >>the below sequence
> >>
> >>for(5000) {
> >>mmap(128M)
> >>touch every page of 2048 page
> >>munmap()
> >>}
> >>
I like the idea of not tracking the slots at all. It is something the
guest should not be knowing or tracking.
> >>The test is run with address randomization off, swap disabled in both host
> >>and guest.
> >>
> >>
> >>|------------+----------+---------------+--------------------------+-----------------------|
> >>| iterations | platform | without patch | With series and no hcall | With
> >>series and hcall |
> >>|------------+----------+---------------+--------------------------+-----------------------|
> >>| 1 | powernv | | 50.818343 |
> >> |
> >>| 2 | powernv | | 50.744123 |
> >> |
> >>| 3 | powernv | | 50.721603 |
> >> |
> >>| 4 | powernv | | 50.739922 |
> >> |
> >>| 5 | powernv | | 50.638555 |
> >> |
> >>| 1 | powernv | 51.388249 | |
> >> |
> >>| 2 | powernv | 51.789701 | |
> >> |
> >>| 3 | powernv | 52.240394 | |
> >> |
> >>| 4 | powernv | 51.432255 | |
> >> |
> >>| 5 | powernv | 51.392947 | |
> >> |
> >>|------------+----------+---------------+--------------------------+-----------------------|
> >>| 1 | pseries | | |
> >> 123.154394 |
> >>| 2 | pseries | | |
> >> 122.253956 |
> >>| 3 | pseries | | |
> >> 117.666344 |
> >>| 4 | pseries | | |
> >> 117.681479 |
> >>| 5 | pseries | | |
> >> 117.735808 |
> >>| 1 | pseries | | 119.424940 |
> >> |
> >>| 2 | pseries | | 117.663078 |
> >> |
> >>| 3 | pseries | | 118.345584 |
> >> |
> >>| 4 | pseries | | 119.620934 |
> >> |
> >>| 5 | pseries | | 119.463185 |
> >> |
> >>| 1 | pseries | 122.810867 | |
> >> |
> >>| 2 | pseries | 115.760801 | |
> >> |
> >>| 3 | pseries | 115.257030 | |
> >> |
> >>| 4 | pseries | 116.617884 | |
> >> |
> >>| 5 | pseries | 117.247036 | |
> >> |
> >>|------------+----------+---------------+--------------------------+-----------------------|
> >>
> >
What does 'With series and no hcall' mean? does it mean -- no calls to new
hcalls,
instead use H_READ_4 followed by old HCALLs?
And I am assuming the code is not using any of my slot-move-to-secondary-pte
changes.
RP
