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Re: [Qemu-devel] [PATCH v2 5/7] exec: memory radix tree page level?compr
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH v2 5/7] exec: memory radix tree page level?compression |
Date: |
Thu, 14 Nov 2013 16:40:37 +0200 |
On Thu, Nov 14, 2013 at 08:54:11AM +0000, Avi Kivity wrote:
> Michael S. Tsirkin <mst <at> redhat.com> writes:
>
> >
> > At the moment, memory radix tree is already variable width, but it can
> > only skip the low bits of address.
> >
> > This is efficient if we have huge memory regions but inefficient if we
> > are only using a tiny portion of the address space.
> >
> > After we have built up the map, detect
> > configurations where a single L2 entry is valid.
> >
> > We then speed up the lookup by skipping one or more levels.
> > In case any levels were skipped, we might end up in a valid section
> > instead of erroring out. We handle this by checking that
> > the address is in range of the resulting section.
> >
>
>
> I think this is overkill. It can be done in a simpler way as follows:
>
>
> phys_page_find(RadixTree* tr, hwaddr index, ...)
> {
> if (index & rt->invalid_index_mask) {
> // not found
> }
> lp = rt->root;
> for (i = rt->nb_levels - 1; i >= 0 && !lp.is_leaf; --i) {
> ...
>
> This exploits the fact the lower portion of the address space is always
> filled, at least in the cases that matter to us.
>
>
>
>
>
Basically skip unused high bits?
Sure.
In fact I think both optimizations can be combined.
--
MST
- [Qemu-devel] [PATCH v2 0/7] making address spaces 64 bit wide, Michael S. Tsirkin, 2013/11/13
- [Qemu-devel] [PATCH v2 1/7] split definitions for exec.c and translate-all.c radix trees, Michael S. Tsirkin, 2013/11/13
- [Qemu-devel] [PATCH v2 2/7] exec: replace leaf with skip, Michael S. Tsirkin, 2013/11/13
- [Qemu-devel] [PATCH v2 3/7] exec: extend skip field to 6 bit, page entry to 32 bit, Michael S. Tsirkin, 2013/11/13
- [Qemu-devel] [PATCH v2 4/7] exec: pass hw address to phys_page_find, Michael S. Tsirkin, 2013/11/13
- [Qemu-devel] [PATCH v2 5/7] exec: memory radix tree page level compression, Michael S. Tsirkin, 2013/11/13
- Re: [Qemu-devel] [PATCH v2 5/7] exec: memory radix tr ee page level compression, Avi Kivity, 2013/11/14
- Re: [Qemu-devel] [PATCH v2 5/7] exec: memory radix tree page level?compression,
Michael S. Tsirkin <=
- Re: [Qemu-devel] [PATCH v2 5/7] exec: memory radix tree page level?compression, Avi Kivity, 2013/11/14
- Re: [Qemu-devel] [PATCH v2 5/7] exec: memory radix tree page level?compression, Michael S. Tsirkin, 2013/11/14
- Re: [Qemu-devel] [PATCH v2 5/7] exec: memory radix tree page level?compression, Avi Kivity, 2013/11/14
- Re: [Qemu-devel] [PATCH v2 5/7] exec: memory radix tree page level?compression, Michael S. Tsirkin, 2013/11/17
- Re: [Qemu-devel] [PATCH v2 5/7] exec: memory radix tree page level?compression, Avi Kivity, 2013/11/17
[Qemu-devel] [PATCH v2 6/7] exec: make address spaces 64-bit wide, Michael S. Tsirkin, 2013/11/13
[Qemu-devel] [PATCH v2 7/7] exec: reduce L2_PAGE_SIZE, Michael S. Tsirkin, 2013/11/13