On Wed, 8 Jul 2020 at 14:48, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote:
>
> We need to make the DMA allocations used for page directories to be
> performed up front so that we can include those allocations in our
> memory reservation pass. The downside is that we have to assume the
> worst case, even before we know the final layout, and always allocate
> enough page directories for this object, even when there will be overlap.
> This unfortunately can be quite expensive, especially as we have to
> clear/reset the page directories and DMA pages, but it should only be
> required during early phases of a workload when new objects are being
> discovered, or after memory/eviction pressure when we need to rebind.
> Once we reach steady state, the objects should not be moved and we no
> longer need to preallocating the pages tables.
>
> It should be noted that the lifetime for the page directories DMA is
> more or less decoupled from individual fences as they will be shared
> across objects across timelines.
>
> v2: Only allocate enough PD space for the PTE we may use, we do not need
> to allocate PD that will be left as scratch.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
<snip>
>
> +static unsigned long pd_count(u64 size, int shift)
> +{
> + /* Beware later misalignment */
> + return (size + 2 * (BIT_ULL(shift) - 1)) >> shift;
> +}
> +
> +int i915_vm_alloc_pt_stash(struct i915_address_space *vm,
> + struct i915_vm_pt_stash *stash,
> + u64 size)
> +{
> + unsigned long count;
> + int shift = 21;
> + int n;
if (gen >= 8)
shift = 21;
else
shift = 22;
?
Since pt=4M, pd=2G with the weird legacy ppgtt stuff?
> +
> + count = pd_count(size, shift);
> + while (count--) {
> + struct i915_page_table *pt;
> +
> + pt = alloc_pt(vm);
> + if (IS_ERR(pt)) {
> + i915_vm_free_pt_stash(vm, stash);
> + return PTR_ERR(pt);
> + }
> +
> + pt->stash = stash->pt[0];
> + stash->pt[0] = pt;
> + }
> +
> + for (n = 1; n < vm->top; n++) {
> + shift += 9;
> + count = pd_count(size, shift);
> + while (count--) {
> + struct i915_page_directory *pd;
> +
> + pd = alloc_pd(vm);
> + if (IS_ERR(pd)) {
> + i915_vm_free_pt_stash(vm, stash);
> + return PTR_ERR(pd);
> + }
> +
> + pd->pt.stash = stash->pt[1];
> + stash->pt[1] = &pd->pt;
> + }
> + }
> +
> + return 0;
> +}
> +
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