[PATCH 8/9] drm/i915/gvt: Manage shadow pages with radix tree

Du, Changbin changbin.du at intel.com
Mon Dec 25 10:16:09 UTC 2017


On Mon, Dec 25, 2017 at 05:35:05PM +0800, Zhi Wang wrote:
> Better attach some investigation and performance data here.
> 
> Radix tree is quite heavy and requires more memory than hash and rb tree. A
> lot of Linux subsystems finally turn to rb tree from radix because of that.
>
Sure? then why page cache still use radix tree? :

> It only shows better performance in a very large scalability, compared to
> hash and RB. So, usually, people tends to use RB tree instead of radix, if
> the hash table is not satisfying.
> 
Here we what we need is a map and radix is it. Most of the rb-tree use cases are
to manage a data with range, like IOVA allocator, VMALLOC and so on.

Actually, here is not so sensitive. Bot rb-tree and radix tree are very quick,
but a little slower than hasn table.

> Thanks,
> Zhi.
> 
> On 12/25/17 17:11, changbin.du at intel.com wrote:
> > From: Changbin Du <changbin.du at intel.com>
> > 
> > We don't know how many page tables will be shadowed. It varies
> > considerably corresponding to guest load. So radix tree is the
> > best choice for us.
> > 
> > Signed-off-by: Changbin Du <changbin.du at intel.com>
> > ---
> >   drivers/gpu/drm/i915/gvt/gtt.c | 48 ++++++++++++++++++++++--------------------
> >   drivers/gpu/drm/i915/gvt/gtt.h |  4 +---
> >   2 files changed, 26 insertions(+), 26 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gvt/gtt.c b/drivers/gpu/drm/i915/gvt/gtt.c
> > index 1866c2d..1ce6393 100644
> > --- a/drivers/gpu/drm/i915/gvt/gtt.c
> > +++ b/drivers/gpu/drm/i915/gvt/gtt.c
> > @@ -638,8 +638,8 @@ static void ppgtt_free_spt(struct intel_vgpu_ppgtt_spt *spt)
> >   	dma_unmap_page(kdev, spt->shadow_page.mfn << I915_GTT_PAGE_SHIFT, 4096,
> >   		       PCI_DMA_BIDIRECTIONAL);
> > -	if (!hlist_unhashed(&spt->node))
> > -		hash_del(&spt->node);
> > +
> > +	radix_tree_delete(&spt->vgpu->gtt.spt_tree, spt->shadow_page.mfn);
> >   	if (spt->guest_page.oos_page)
> >   		detach_oos_page(spt->vgpu, spt->guest_page.oos_page);
> > @@ -652,12 +652,14 @@ static void ppgtt_free_spt(struct intel_vgpu_ppgtt_spt *spt)
> >   static void ppgtt_free_all_spt(struct intel_vgpu *vgpu)
> >   {
> > -	struct hlist_node *n;
> >   	struct intel_vgpu_ppgtt_spt *spt;
> > -	int i;
> > +	struct radix_tree_iter iter;
> > +	void **slot;
> > -	hash_for_each_safe(vgpu->gtt.spt_hash_table, i, n, spt, node)
> > +	radix_tree_for_each_slot(slot, &vgpu->gtt.spt_tree, &iter, 0) {
> > +		spt = radix_tree_deref_slot(slot);
> >   		ppgtt_free_spt(spt);
> > +	}
> >   }
> >   static int ppgtt_handle_guest_write_page_table_bytes(
> > @@ -695,16 +697,10 @@ static struct intel_vgpu_ppgtt_spt *intel_vgpu_find_spt_by_gfn(
> >   }
> >   /* Find the spt by shadow page mfn. */
> > -static struct intel_vgpu_ppgtt_spt *intel_vgpu_find_spt_by_mfn(
> > +static inline struct intel_vgpu_ppgtt_spt *intel_vgpu_find_spt_by_mfn(
> >   		struct intel_vgpu *vgpu, unsigned long mfn)
> >   {
> > -	struct intel_vgpu_ppgtt_spt *spt;
> > -
> > -	hash_for_each_possible(vgpu->gtt.spt_hash_table, spt, node, mfn) {
> > -		if (spt->shadow_page.mfn == mfn)
> > -			return spt;
> > -	}
> > -	return NULL;
> > +	return radix_tree_lookup(&vgpu->gtt.spt_tree, mfn);
> >   }
> >   static int reclaim_one_ppgtt_mm(struct intel_gvt *gvt);
> > @@ -739,8 +735,8 @@ static struct intel_vgpu_ppgtt_spt *ppgtt_alloc_spt(
> >   			     0, 4096, PCI_DMA_BIDIRECTIONAL);
> >   	if (dma_mapping_error(kdev, daddr)) {
> >   		gvt_vgpu_err("fail to map dma addr\n");
> > -		free_spt(spt);
> > -		return ERR_PTR(-EINVAL);
> > +		ret = -EINVAL;
> > +		goto err_free_spt;
> >   	}
> >   	spt->shadow_page.vaddr = page_address(spt->shadow_page.page);
> >   	spt->shadow_page.mfn = daddr >> I915_GTT_PAGE_SHIFT;
> > @@ -753,17 +749,23 @@ static struct intel_vgpu_ppgtt_spt *ppgtt_alloc_spt(
> >   	ret = intel_vgpu_register_page_track(vgpu, spt->guest_page.gfn,
> >   					ppgtt_write_protection_handler, spt);
> > -	if (ret) {
> > -		free_spt(spt);
> > -		dma_unmap_page(kdev, daddr, PAGE_SIZE, PCI_DMA_BIDIRECTIONAL);
> > -		return ERR_PTR(ret);
> > -	}
> > +	if (ret)
> > +		goto err_unmap_dma;
> > -	INIT_HLIST_NODE(&spt->node);
> > -	hash_add(vgpu->gtt.spt_hash_table, &spt->node, spt->shadow_page.mfn);
> > +	ret = radix_tree_insert(&vgpu->gtt.spt_tree, spt->shadow_page.mfn, spt);
> > +	if (ret)
> > +		goto err_unreg_page_track;
> >   	trace_spt_alloc(vgpu->id, spt, type, spt->shadow_page.mfn, gfn);
> >   	return spt;
> > +
> > +err_unreg_page_track:
> > +	intel_vgpu_unregister_page_track(vgpu, spt->guest_page.gfn);
> > +err_unmap_dma:
> > +	dma_unmap_page(kdev, daddr, PAGE_SIZE, PCI_DMA_BIDIRECTIONAL);
> > +err_free_spt:
> > +	free_spt(spt);
> > +	return ERR_PTR(ret);
> >   }
> >   #define pt_entry_size_shift(spt) \
> > @@ -1965,7 +1967,7 @@ int intel_vgpu_init_gtt(struct intel_vgpu *vgpu)
> >   {
> >   	struct intel_vgpu_gtt *gtt = &vgpu->gtt;
> > -	hash_init(gtt->spt_hash_table);
> > +	INIT_RADIX_TREE(&gtt->spt_tree, GFP_KERNEL);
> >   	INIT_LIST_HEAD(&gtt->ppgtt_mm_list_head);
> >   	INIT_LIST_HEAD(&gtt->oos_page_list_head);
> > diff --git a/drivers/gpu/drm/i915/gvt/gtt.h b/drivers/gpu/drm/i915/gvt/gtt.h
> > index 32504c0..c006cc9d 100644
> > --- a/drivers/gpu/drm/i915/gvt/gtt.h
> > +++ b/drivers/gpu/drm/i915/gvt/gtt.h
> > @@ -39,7 +39,6 @@
> >   struct intel_vgpu_mm;
> > -#define INTEL_GVT_GTT_HASH_BITS 8
> >   #define INTEL_GVT_INVALID_ADDR (~0UL)
> >   struct intel_gvt_gtt_entry {
> > @@ -179,7 +178,7 @@ struct intel_vgpu_gtt {
> >   	struct intel_vgpu_mm *ggtt_mm;
> >   	unsigned long active_ppgtt_mm_bitmap;
> >   	struct list_head ppgtt_mm_list_head;
> > -	DECLARE_HASHTABLE(spt_hash_table, INTEL_GVT_GTT_HASH_BITS);
> > +	struct radix_tree_root spt_tree;
> >   	struct list_head oos_page_list_head;
> >   	struct list_head post_shadow_list_head;
> >   	struct intel_vgpu_scratch_pt scratch_pt[GTT_TYPE_MAX];
> > @@ -212,7 +211,6 @@ struct intel_vgpu_oos_page {
> >   struct intel_vgpu_ppgtt_spt {
> >   	atomic_t refcount;
> >   	struct intel_vgpu *vgpu;
> > -	struct hlist_node node;
> >   	struct {
> >   		intel_gvt_gtt_type_t type;
> > 
> _______________________________________________
> intel-gvt-dev mailing list
> intel-gvt-dev at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gvt-dev

-- 
Thanks,
Changbin Du


More information about the intel-gvt-dev mailing list