First, you need to run it twice, see
http://docs.julialang.org/en/latest/manual/profile/#memory-allocation-analysis
and the part about clear_malloc_data.
Second, I think you have a bug:
size(s::UnsafeSlice) = size(s.size)
should presumably be
size(s::UnsafeSlice) = s.size
--Tim
On Monday, April 20, 2015 09:35:33 AM Peter Brady wrote:
> Here's the results of running --track-allocation=user --inline=no on 0.4.
> Note that I also deleted all the macros which were affecting the reported
> line numbers.
>
> I have three questions base on the data below:
> 1. Why is the call to size which indexes into a tuple so expensive
> 2. Why is setindex! so expensive?
> 3. Why is it so expensive to update the 'start' attribute of my
> unsafeslice?
> Does anyone have any answers or any suggestions on what tools to use to
> find the answers?
>
> Here's my session:
>
>
> $ ~/gitrepos/julia0.4/julia --track-allocation=user --inline=no
> _
> _ _ _(_)_ | A fresh approach to technical computing
> (_) | (_) (_) | Documentation: http://docs.julialang.org
> _ _ _| |_ __ _ | Type "help()" for help.
>
> | | | | | | |/ _` | |
> | | |
> | | |_| | | | (_| | | Version 0.4.0-dev+4385 (2015-04-20 14:52 UTC)
>
> _/ |\__'_|_|_|\__'_| | Commit 5499882 (0 days old master)
>
> |__/ | x86_64-redhat-linux
>
> julia> include("test_alloc.jl")
> test_unsafe (generic function with 2 methods)
>
>
> julia> test_unsafe(1);
>
>
> julia>
> [ptb@cyrus julia]$
>
>
> And the output
>
>
> - using ArrayViews
> - import Base: size, getindex, setindex!, ndims, start, stride,
> pointer
> -
> - type UnsafeSlice{T,N, P<:Ptr} <: AbstractArray
> - start::Int
> - stride::Int
> - size::NTuple{N,Int}
> - p::P
> - end
> -
> - size(s::UnsafeSlice) = size(s.size)
> -
> 7356448 size(s::UnsafeSlice, i::Int) = s.size[i]
> -
> - ndims{T,N}(s::UnsafeSlice{T,N}) = N
> -
> - getindex(s::UnsafeSlice, i::Int) = unsafe_load(s.p, s.start+(i-1)*
> s.stride)
> -
> 1048559648 setindex!(s::UnsafeSlice, x, i::Int) = unsafe_store!(s.p, x, s.
> start+(i-1)*s.stride)
> -
> - function UnsafeSlice(a, slicedim::Int, start=1)
> 0 p = pointer(a)
> -
> 0 str = stride(a, slicedim)
> -
> 368 UnsafeSlice{eltype(a), ndims(a), typeof(p)}(start, str, size(a
> ),p)
> - end
> -
> - function update(a::UnsafeSlice, idx, off)
> -
> 0 for i=1:size(a, idx)
> -
> 0 a[i] = -10*off+i
> - end
> -
> 0 a
> - end
> -
> - function setk_UnSafe{T}(a::Array{T,3})
> 0 us = UnsafeSlice(a, 3)
> -
> 0 for j=1:size(a,2),i=1:size(a,1)
> -
> 14712896 us.start = sub2ind(size(a), i, j, 1)
> -
> 0 update(us, 3, us.start)
> - end
> -
> 0 a
> - end
> -
> - function test_unsafe(n, time=true)
> 0 a = zeros(Int, (320, 320, 320))
> -
> - # warmup
> 0 setk_UnSafe(a);
> -
> 0 Profile.clear_malloc_data()
> -
> 0 for i=1:n
> -
> 0 setk_UnSafe(a)
> -
> - end
> -
> 0 a
> - end
> -
>
> On Monday, April 20, 2015 at 9:04:41 AM UTC-6, Peter Brady wrote:
> > Accidentally hit reply instead of reply-all. Sorry for the double post.
> >
> > Ran my script in 0.4 and got these results...
> >
> > julia> test_all(5)
> > test_stride
> > elapsed time: 2.008043041 seconds (0 bytes allocated)
> > test_view
> > elapsed time: 8.871387399 seconds (42 MB allocated, 0.23% gc time in 2
> > pauses with 1 full sweep)
> > test_unsafe
> > elapsed time: 2.308598574 seconds (46 MB allocated, 0.68% gc time in 2
> > pauses with 1 full sweep)
> > test_unsafeview
> > elapsed time: 9.106651158 seconds (0 bytes allocated)
> >
> > julia> test_all(10)
> > test_stride
> > elapsed time: 4.012240175 seconds (0 bytes allocated)
> > test_view
> > elapsed time: 18.085514211 seconds (85 MB allocated, 0.16% gc time in 4
> > pauses with 1 full sweep)
> > test_unsafe
> > elapsed time: 4.477773618 seconds (93 MB allocated, 1.12% gc time in 4
> > pauses with 1 full sweep)
> > test_unsafeview
> > elapsed time: 18.146163969 seconds (0 bytes allocated)
> >
> > So the allocation for the new unsafeview has been reduced to zero but it
> > has become slower than the regular view.
> >
> > Perhaps the compiler optimizations that have been discussed here are
> > occuring since the only occurence of 'unsafeview' is the argument to a
> > function.
> >
> > On Mon, Apr 20, 2015 at 12:57 AM, René Donner <li...@donner.at> wrote:
> >> What about something like unsafe_updateview!(view, indices...) ?
> >>
> >> It could be used like this (pseudocode):
> >> view = unsafe_view(data, 1, 1, :) # to construct / allocate
> >> for i in ..., j in ...
> >>
> >> unsafe_updateview!(view, i, j, :)
> >> # use view
> >>
> >> end
> >>
> >> In the trivial case of unsafe_view(data, :, :, i) this would boil down to
> >> a single pointer update. Of course passing around these views outside of
> >> their scope is rather discouraged. I use this pattern a lot and it proved
> >> to be very handy / fast.
> >>
> >> Am 20.04.2015 um 02:08 schrieb Dahua Lin <linda...@gmail.com>:
> >> > My benchmark shows that element indexing has been as fast as it can be
> >>
> >> for array views (or subarrays in Julia 0.4).
> >>
> >> > Now the problem is actually the construction of views/subarrays. To
> >>
> >> optimize the overhead of this part, the compiler may need to introduce
> >> additional optimization.
> >>
> >> > Dahua
> >> >
> >> >
> >> > On Monday, April 20, 2015 at 6:39:35 AM UTC+8, Sebastian Good wrote:
> >> > —track-allocation still requires guesswork, as optimizations can move
> >>
> >> the allocation to a different place than you would expect.
> >>
> >> > On April 19, 2015 at 4:36:19 PM, Peter Brady (peter...@gmail.com)
> >>
> >> wrote:
> >> >> So I discovered the --track-allocation option and now I am really
> >>
> >> confused:
> >> >> Here's my session:
> >> >>
> >> >> $ julia --track-allocation=all
> >> >>
> >> >> _
> >> >>
> >> >> _ _ _(_)_ | A fresh approach to technical computing
> >> >>
> >> >> (_) | (_) (_) | Documentation: http://docs.julialang.org
> >> >>
> >> >> _ _ _| |_ __ _ | Type "help()" for help.
> >> >>
> >> >> | | | | | | |/ _` | |
> >> >> | | |
> >> >> | | |_| | | | (_| | | Version 0.3.8-pre+13 (2015-04-17 18:08 UTC)
> >> >>
> >> >> _/ |\__'_|_|_|\__'_| | Commit 0df962d* (2 days old release-0.3)
> >> >>
> >> >> |__/ | x86_64-redhat-linux
> >> >>
> >> >> julia> include("test.jl")
> >> >> test_all (generic function with 1 method)
> >> >>
> >> >> julia> test_unsafe(5)
> >> >>
> >> >> And here's the relevant part of the resulting test.jl.mem file. Note
> >>
> >> that I commented out some calls to 'size' and replaced with the
> >> appropriate
> >> hard-coded values but the resulting allocation is the same... Can anyone
> >> shed some light on this while I wait for 0.4 to compile?
> >>
> >> >> - function update(a::AbstractArray, idx, off)
> >> >>
> >> >> 8151120 for i=1:320 #size(a, idx)
> >> >>
> >> >> 0 a[i] = -10*off+i
> >> >> - end
> >> >> 0 a
> >> >> - end
> >> >> -
> >> >>
> >> >> - function setk_UnSafe{T}(a::Array{T,3})
> >> >>
> >> >> 760 us = UnsafeSlice(a, 3)
> >> >>
> >> >> 0 for j=1:size(a,2),i=1:size(a,1)
> >> >>
> >> >> 8151120 us.start = (j-1)*320+i #size(a,1)+i
> >> >>
> >> >> - #off = sub2ind(size(a), i, j, 1)
> >> >> 0 update(us, 3, us.start)
> >> >> - end
> >> >> 0 a
> >> >> - end
> >> >> - function test_unsafe(n)
> >> >> 0 a = zeros(Int, (320, 320, 320))
> >> >> - # warmup
> >> >> 0 setk_UnSafe(a);
> >> >> 0 clear_malloc_data()
> >> >> - #@time (
> >> >> 0 for i=1:n; setk_UnSafe(a); end
> >> >> - end
> >> >>
> >> >> On Sunday, April 19, 2015 at 2:21:56 PM UTC-6, Peter Brady wrote:
> >> >> @Dahua, thanks for adding an unsafeview! I appreciate how quickly
> >>
> >> this community responds.
> >>
> >> >> I've added the following function to my test.jl script
> >> >> function setk_unsafeview{T}(a::Array{T,3})
> >> >>
> >> >> for j=1:size(a,2),i=1:size(a,1)
> >> >>
> >> >> off = sub2ind(size(a), i, j, 1)
> >> >> update(unsafe_view(a, i, j, :), 3, off)
> >> >>
> >> >> end
> >> >> a
> >> >>
> >> >> end
> >> >>
> >> >> But I'm not seeing the large increase in performance I was
> >>
> >> expecting. My timings are now
> >>
> >> >> julia> test_all(5);
> >> >> test_stride
> >> >> elapsed time: 2.156173128 seconds (0 bytes allocated)
> >> >> test_view
> >> >> elapsed time: 9.30964534 seconds (94208000 bytes allocated, 0.47% gc
> >>
> >> time)
> >>
> >> >> test_unsafe
> >> >> elapsed time: 2.169307471 seconds (16303000 bytes allocated)
> >> >> test_unsafeview
> >> >> elapsed time: 8.955876793 seconds (90112000 bytes allocated, 0.41% gc
> >>
> >> time)
> >>
> >> >> To be fair, I am cheating a bit with my custom 'UnsafeSlice' since I
> >>
> >> make only one instance and simply update the offset on each iteration.
> >> If
> >> I make it immutable and create a new instance on every iteration (as I do
> >> for the view and unsafeview), things slow down a little and the
> >> allocation
> >>
> >> goes south:
> >> >> julia> test_all(5);
> >> >> test_stride
> >> >> elapsed time: 2.159909265 seconds (0 bytes allocated)
> >> >> test_view
> >> >> elapsed time: 9.029025282 seconds (94208000 bytes allocated, 0.43% gc
> >>
> >> time)
> >>
> >> >> test_unsafe
> >> >> elapsed time: 2.621667854 seconds (114606240 bytes allocated, 2.41% gc
> >>
> >> time)
> >>
> >> >> test_unsafeview
> >> >> elapsed time: 8.888434466 seconds (90112000 bytes allocated, 0.44% gc
> >>
> >> time)
> >>
> >> >> These are all with 0.3.8-pre. I'll try compiling master and see what
> >>
> >> happens. I'm still confused about why allocating a single type with a
> >> pointer, 2 ints and a tuple costs so much memory though.
> >>
> >> >> On Sunday, April 19, 2015 at 11:38:17 AM UTC-6, Tim Holy wrote:
> >> >> It's not just escape analysis, as this (new) issue demonstrates:
> >> >> https://github.com/JuliaLang/julia/issues/10899
> >> >>
> >> >> --Tim
> >> >>
> >> >> On Sunday, April 19, 2015 12:33:51 PM Sebastian Good wrote:
> >> >> > Their size seems much decreased. I’d imagine to totally avoid
> >>
> >> allocation in
> >>
> >> >> > this benchmark requires an optimization that really has nothing to
> >>
> >> do with
> >>
> >> >> > subarrays per se. You’d have to do an escape analysis and see that
> >>
> >> Aj never
> >>
> >> >> > left sumcols. Not easy in practice, since it’s passed to slice and
> >>
> >> length,
> >>
> >> >> > and you’d have to make sure they didn’t squirrel it away or pass it
> >>
> >> on to
> >>
> >> >> > someone else. Then you could stack allocate it, or even destructure
> >>
> >> it into
> >>
> >> >> > a bunch of scalar mutations on the stack. After eliminating dead
> >>
> >> code,
> >>
> >> >> > you’d end up with a no-allocation loop much like you’d write by
> >>
> >> hand. This
> >>
> >> >> > sort of optimization seems to be quite tricky for compilers to pull
> >>
> >> off,
> >>
> >> >> > but it’s a common pattern in numerical code.
> >> >> >
> >> >> > In Julia is such cleverness left entirely to LLVM, or are there
> >>
> >> optimization
> >>
> >> >> > passes in Julia itself? On April 19, 2015 at 6:49:21 AM, Tim Holy
> >> >> > (tim....@gmail.com) wrote:
> >> >> >
> >> >> > Sorry to be slow to chime in here, but the tuple overhaul has landed
> >>
> >> and
> >>
> >> >> > they are still not zero-cost:
> >> >> >
> >> >> > function sumcols(A)
> >> >> > s = 0.0
> >> >> > for j = 1:size(A,2)
> >> >> > Aj = slice(A, :, j)
> >> >> > for i = 1:length(Aj)
> >> >> > s += Aj[i]
> >> >> > end
> >> >> > end
> >> >> > s
> >> >> > end
> >> >> >
> >> >> > Even in the latest 0.4, this still allocates memory. On the other
> >>
> >> hand,
> >>
> >> >> > while SubArrays allocate nearly 2x more memory than ArrayViews, the
> >>
> >> speed
> >>
> >> >> > of the two (replacing `slice` with `view` above) is, for me, nearly
> >> >> > identical.
> >> >> >
> >> >> > --Tim
> >> >> >
> >> >> > On Friday, April 17, 2015 08:30:27 PM Sebastian Good wrote:
> >> >> > > This was discussed a few weeks ago
> >>
> >> https://groups.google.com/d/msg/julia-users/IxrvV8ABZoQ/uWZu5-IB3McJ
> >>
> >> >> > > I think the bottom line is that the current implementation
> >>
> >> *should* be
> >>
> >> >> > > 'zero-cost' once a set of planned improvements and optimizations
> >>
> >> take
> >>
> >> >> > > place. One of the key ones is a tuple overhaul.
> >> >> > >
> >> >> > > Fair to say it can never be 'zero' cost since there is different
> >>
> >> inherent
> >>
> >> >> > > overhead depending on the type of subarray, e.g. offset, slice,
> >> >> > > re-dimension, etc. however the implementation is quite clever
> >> >> > > about
> >> >> > > allowing specialization of those.
> >> >> > >
> >> >> > > In a common case (e.g. a constant offset or simple stride) my
> >> >> > > understanding
> >> >> > > is that the structure will be type-specialized and likely stack
> >>
> >> allocated
> >>
> >> >> > > in many cases, reducing to what you'd write by hand. At least this
> >>
> >> is what
> >>
> >> >> > > they're after.
> >> >> > >
> >> >> > > On Friday, April 17, 2015 at 4:24:14 PM UTC-4, Peter Brady wrote:
> >> >> > > > Thanks for the links. I'll check out ArrayViews as it looks like
> >>
> >> what I
> >>
> >> >> > > > was going to do manually without wrapping it in a type.
> >> >> > > >
> >> >> > > > By semi-dim agnostic I meant that the differencing algorithm
> >>
> >> itself only
> >>
> >> >> > > > cares about one dimension but that dimension is different for
> >>
> >> different
> >>
> >> >> > > > directions. Only a few toplevel routines actually need to know
> >>
> >> about the
> >>
> >> >> > > > dimensionality of the problem.
> >> >> > > >
> >> >> > > > On Friday, April 17, 2015 at 2:04:39 PM UTC-6, René Donner
wrote:
> >> >> > > >> As far as I have measured it sub in 0.4 is still not cheap, as
> >>
> >> it
> >>
> >> >> > > >> provides the flexibility to deal with all kinds of strides and
> >>
> >> offsets,
> >>
> >> >> > > >> and
> >> >> > > >> the view object itself thus has a certain size. See
> >> >> > > >> https://github.com/rened/FunctionalData.jl#efficiency for a
> >>
> >> simple
> >>
> >> >> > > >> analysis, where the speed is mostly dominated by the speed of
> >>
> >> the
> >>
> >> >> > > >> "sub-view" mechanism.
> >> >> > > >>
> >> >> > > >> To get faster views which require strides etc you can try
> >> >> > > >> https://github.com/JuliaLang/ArrayViews.jl
> >> >> > > >>
> >> >> > > >> What do you mean by semi-dim agnostic? In case you only need
> >>
> >> indexing
> >>
> >> >> > > >> along the last dimension (like a[:,:,i] and a[:,:,:,i]) you can
> >>
> >> use
> >>
> >>
> >> https://github.com/rened/FunctionalData.jl#efficient-views-details
> >>
> >> >> > > >> which uses normal DenseArrays and simple pointer updates
> >>
> >> internally. It
> >>
> >> >> > > >> can also update a view in-place, by just incrementing the
> >>
> >> pointer.
> >>
> >> >> > > >> Am 17.04.2015 um 21:48 schrieb Peter Brady <peter...@gmail.com
> >> >> > > >>
> >> >> > > >> > Inorder to write some differencing algorithms in a
> >>
> >> semi-dimensional
> >>
> >> >> > > >> agnostic manner the code I've written makes heavy use of
> >>
> >> subarrays
> >>
> >> >> > > >> which
> >> >> > > >> turn out to be rather costly. I've noticed some posts on the
> >>
> >> cost of
> >>
> >> >> > > >> subarrays here and that things will be better in 0.4. Can
> >>
> >> someone
> >>
> >> >> > > >> comment
> >> >> > > >> on how much better? Would subarray (or anything like it) be on
> >>
> >> par with
> >>
> >> >> > > >> simply passing an offset and stride (constant) and computing
> >>
> >> the index
> >>
> >> >> > > >> myself? I'm currently using the 0.3 release branch.
