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    SubjectRe: [RFT][PATCH v2 3/9] vfio/ccw: Only pass in contiguous pages
    On Tue, Jul 05, 2022 at 11:27:53PM -0700, Nicolin Chen wrote:
    > This driver is the only caller of vfio_pin/unpin_pages that might pass
    > in a non-contiguous PFN list, but in many cases it has a contiguous PFN
    > list to process. So letting VFIO API handle a non-contiguous PFN list
    > is actually counterproductive.
    >
    > Add a pair of simple loops to pass in contiguous PFNs only, to have an
    > efficient implementation in VFIO.
    >
    > Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
    > ---
    > drivers/s390/cio/vfio_ccw_cp.c | 70 +++++++++++++++++++++++++++-------
    > 1 file changed, 56 insertions(+), 14 deletions(-)

    I think this is fine as-is for this series, but someone who knows and
    can test ccw should go in and fix things so that pfn_array_alloc()
    doesn't exist. Allocating memory and filling it with consecutive
    integers is kind of silly given we can just call vfio_pin_pages() with
    pa_nr directly.

    pa->pa_iova_pfn[0] = pa->pa_iova >> PAGE_SHIFT;
    pa->pa_pfn[0] = -1ULL;
    for (i = 1; i < pa->pa_nr; i++) {
    pa->pa_iova_pfn[i] = pa->pa_iova_pfn[i - 1] + 1;

    It looks like only the 'ccw_is_idal' flow can actually create
    non-continuities. Also the loop in copy_from_iova() should ideally be
    using the much faster 'rw' interface, and not a pin/unpin cycle just
    to memcpy.

    If I guess right these changes would significantly speed this driver
    up.

    Anyhow,

    Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

    Jason

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