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+
+<div class=leader>
+<i class="twa twa-rocket"></i>
+<i class="twa twa-rocket"></i>
+<i class="twa twa-rocket"></i>
+<i class="twa twa-rocket"></i>
+<br>
+Parallel Julia
+</div>
+
+
+
+# Usual ways to gain performance:
+
+1. Do not work on data that is too far *(cache)*
+2. Do not waste energy on organizing trivial stuff *(SIMD/SIMT)*
+3. Do not waste time waiting for data *(HT/GPU)*
+4. Organize the computation so that more computers don't trip over each other on the task *(SMP)*
+5. Move the computers closer to data *(distributed computing)*
+
+Let's spend a moment explaining these technologies...
+
+
+
+# Data distance and physical limits
+
+<div class=leader>
+How far does light go in 1 cycle of a 3GHz CPU?
+</div>
+
+
+
+# CPUs vs GPUs (SIMD vs SIMT)
+
+<center>
+<img src="slides/img/cpu.png" width="40%" />
+<img src="slides/img/gpu.png" width="40%" />
+</center>
+
+
+
+# SIMD problem: Your Data Looks Like Thisâ„¢
+
+<center>
+<img src="slides/img/maze.jpg" width="75%" />
+</center>
+
+
+
+# Parallel programming
+
+<center>
+<img src="slides/img/threads.jpeg" width="50%" /><br>
+(notice the false sharing at threaddog 5)
+</center>
+
+Distributed computing can give you:
+
+- more memory
+- more total memory bandwidth (!)
+- more synchronization problems
+
+
+
+# Julia tools
+
+Let's implement a matrix multiplication manually, and try:
+
+- checking if SIMD instructions are used
+- reordering the loops
+- using smaller floats
+- tiling
+- `@threads`
+
+<center><img src="slides/img/tiling.jpeg" width="33%" /></center>
+
+
+
+# Distributed computing with Julia
+
+```julia
+using Distributed
+addprocs(10)
+
+pmap(myfunction, mydata, workers=workers())
+```
+
+(Spoiler: you can add processes on remote machines using SSH.)
+
+
+
+# Distributed computing with Julia (on the HPC)
+
+```julia
+using Distributed, ClusterManagers
+addprocs_slurm(parse(Int, ENV["SLURM_NTASKS"]))
+
+pmap(myfunction, mydata, workers=workers())
+```
+
+You typically want to load the data locally at the workers.
+
+For more complex schemes:
+- `Dagger.jl` provides complex synchronization/task dependency schemes
+- `DistributedData.jl` provides primitives for manipulating the data precisely
+
+
+
+# How to use a GPU?
+
+```julia
+using CUDA
+
+A = cu(randn(1000,1000));
+B = cu(randn(1000,1000));
+A = A * B;
+```
+
+...transparently uses CUDA, cuBLAS, cuSPARSE, cuDNN and many other libraries to do stuff quicker.
+
+
+
+# How to actually program a GPU?
+
+CUDA.jl can compile Julia code into CUDA kernel code.
+
+```julia
+function fill_with_indexes!(array)
+ index = threadIdx().x + blockDim().x * (blockIdx().x - 1)
+ stride = gridDim().x * blockDim().x
+ for i = index:stride:length(arr)
+ arr[i] = i
+ end
+ return
+end
+
+A = cu(zeros(9999999))
+@cuda threads=1024 blocks=16 fill_with_indexes!(A)
+```
+
+
+
+# Homeworks
+
+## Homework 2 update
+
+Feel free to apply whatever we did today for bonus points.
+
+- think about cache efficiency
+- remember that most forces are repulsive forces
+- `@threads` may help for larger graphs
+
+## Homework 3
+
+- We will learn to handle ugly and hairy data.
+- Last lecture is going to go over the methodology, but you can try earlier.
+
+
+
+# Homework 3
+
+We will simulate a cookie distribution network:
+- there's one central *cookie factory*
+- cookie *transports* move cookies in loads of N cookies
+ - they require 1 cookie to sustain themselves for each batch of cookies transported
+ - N is different for each transport
+- cookie *distribution points* divide incoming cookies among next paths in networks
+ - exact distribution ratio among the paths
+ - no cookies consumed
+- cookie *munchers* are at the end of the transport chain
+ - each of them munches N cookies per day (again different for each muncher)
+
+
+
+# Homework 3 (Data)
+
+```json
+{ type: "distribution point",
+ serves: [
+ { type: "muncher", consumption: 3 },
+ { type: "transport",
+ capacity: 5,
+ serves: {
+ type: "distribution point",
+ serves: [
+ { type: "muncher", consumption: 7 },
+ { type: "muncher", consumption: 2 },
+ { type: "muncher", consumption: 1 }
+ ]
+ ratios: [1,1,1]
+ }
+ }
+ ],
+ ratios: [1,5]
+}
+```
+
+Pretty-printed (one possibility):
+```
+1 -> munch 3
+5 -> transport 5 -> 1 -> munch 7
+ 1 -> munch 2
+ 1 -> munch 1
+```
+
+
+
+# Homework 3 (Assignment)
+
+Tasks:
+- read the cookie network from a JSON file (we'll provide example data, use `JSON.jl`)
+- make a nice data structure to hold this problem, make sure the input is valid
+- make functions that:
+ - find the length of the *longest chain* (by transport "steps") from the factory to the muncher
+ - find out how many cookies the factory needs to produce daily so that *all munchers are fed*
+ - construct a network where all *transports are split in half*, each half with half cookie consumption
+ - find out *how many cookies are wasted* by being routed to munchers who can't eat them
+ - construct a network where the *distribution points are balanced* so that no cookies get wasted
+ - *BONUS: print the network nicely*
+- for simplicity, data structures and functions may be recursive
+ - performance optimization _is not_ a goal
+ - nice short code _is_ a goal
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+
+# Programming with Julia
+
+## March 2023
+
+<div style="top: 6em; left: 0%; position: absolute;">
+ <img src="theme/img/lcsb_bg.png">
+</div>
+
+<div style="top: 1em; left: 60%; position: absolute;">
+ <img src="slides/img/julia.svg" height="200px">
+ <h1 style="margin-top:3ex; margin-bottom:3ex;">5: Performance and parallelism</h1>
+ <h4>
+ Miroslav KratochvÃl<br>
+ Laurent Heirendt<br>
+ LCSB, DSSE<br>
+ </h4>
+</div>
+
+<link rel="stylesheet" href="https://lcsb-biocore.github.io/icons-mirror/twemoji-amazing.css">
+<style>
+ code {border: 2pt dotted #f80; padding: .4ex; border-radius: .7ex; color:#444; }
+ .reveal pre code {border: 0; font-size: 18pt; line-height:27pt;}
+ em {color: #e02;}
+ li {margin-bottom: 1ex;}
+ div.leader {font-size:400%; line-height:120%; font-weight:bold; margin: 1em;}
+ section {padding-bottom: 10em;}
+</style>
diff --git a/2023/2023-03-21_ProgrammingWithJulia-5/slides/list.json b/2023/2023-03-21_ProgrammingWithJulia-5/slides/list.json
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+[
+ { "filename": "index.md" },
+ { "filename": "5a-para.md" }
+]