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24-core CPU and I can’t move my mouse
This story begins, as they so often do, when I noticed that my machine was behaving poorly. My Windows 10 work machine has 24 cores (48 hyper-threads) and they were 50% idle. It has 64 GB of RAM an…
Bruce Dawson
Forecast for randomascii: programming, tech topics, with a chance of unicycling
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Why modern software is slow
I apologize for this title because there are many things that can make modern software slow. Blindly applying one explanation without a bit of investigation is the software equivalent of a cargo cu…
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24-core CPU and I can’t type an email
I wasn’t looking for trouble. I wasn’t trying to compile a huge project in the background (24-core CPU and I can’t move my mouse), I was just engaging in that most mundane of 21st century tasks, wr…
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Finding a CPU Design Bug in the Xbox 360
The recent reveal of Meltdown and Spectre reminded me of the time I found a related design bug in the Xbox 360 CPU – a newly added instruction whose mere existence was dangerous. Back in 2005 I was…
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There are only four billion floats, so test them all (2014)
A few months ago I saw a blog post touting fancy new SSE3 functions for implementing vector floor, ceil, and round functions. There was the inevitable proud proclaiming of impressive performance an…
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O(n^2), again, now in Windows Management Instrumentation
I recently hit some multi-minute delays on my workstation. After investigating I found that the problem was due to a lock being held for five minutes, and during that time the lock-holder was mostl…
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63 Cores Blocked by Seven Instructions
I seem to have a habit of writing about super powerful machines whose many cores are laid low by misuse of locks. So. Yeah. It’s that again. But this one seems particularly impressive. I mean, how …
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No Start Menu for You
I tend to launch most programs on my Windows 10 laptop by typing the <Win> key, then a few letters of the program name, and then hitting enter. On my powerful laptop (SSD and 32 GB of RAM) th…
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Intel Underestimates Error Bounds by 1.3 Quintillion
Intel’s manuals for their x86/x64 processor clearly state that the fsin instruction (calculating the trigonometric sine) has a maximum error, in round-to-nearest mode, of one unit in the last place…
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Arranging Invisible Icons in Quadratic Time
Near the end of January I was pointed to a twitter thread where a Windows user with a powerful machine was hitting random hangs in explorer. Lots of unscientific theories were being proposed. I don…
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5.5 mm in 1.25 nanoseconds
In 2004 I was working for Microsoft in the Xbox group, and a new console was being created. I got a copy of the detailed descriptions of the Xbox 360 CPU and I read it through multiple times and su…
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Life, death, and retirement
I haven’t been blogging much lately, and it turns out there is a very good reason.My last technical blog post was October 1st of last year. After I hit publish on that one I went to get ready for b…
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A Not-Called Function Can Cause a 5X Slowdown
Subtitle: Making Windows Slower Part 3: Process Destruction In the summer of 2017 I wrestled with a Windows performance problem. Process destruction was slow, serialized, and was blocking the syste…
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You Got Your Web Browser in my Compiler
I recently discovered that Microsoft’s VC++ compiler loads mshtml.dll – also known as Internet Explorer. The compiler does this whenever the /analyze option (requesting static code analysis) is use…
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24-core CPU and I can’t type an email – part two
In my last post I promised to give more details about some rabbit holes that I went down during the investigation, including page tables, locks, WMI, and a vmmap bug. Those details are here, along …
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Compiler bug? Linker bug? Windows Kernel bug
See the end of the post for an October 2018 bug fix update, or read the whole story: Flaky failures are the worst. In this particular investigation, which spanned twenty months, we suspected hardwa…
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Please restore our registers when you’re done with them
“Hey, you. Yes you, that function over there. When you’re cleaning up please remember to restore all of my registers. Yes, that one too – what do you think this is, Linux?”That’s the problem I was …
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Hey Synaptics, Can You Please Stop Polling
TL;DR – be wary of buying a Lenovo laptop or any other laptop that uses a Synaptics touch pad until Synaptics ships a fixed driver. Their driver has a memory leak and they have a battery-life bug t…
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ARM and Lock-Free Programming
I was inspired by the release of Apple’s M1 ARM processor to tweet about the perils of lock-free programming which led to some robust discussion. The discussion went pretty well given the inanity o…
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Power Wastage on an Idle Laptop
Ever since I upgraded to Windows 10 it’s felt like my battery life is worse. My suspicion was various scanning tasks that were springing to life more frequently, but it was just a hunch. So, …
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Finding Windows HANDLE leaks, in Chromium and others
Three years ago I found a 32 GB memory leak caused by CcmExec.exe failing to close process handles. That bug is fixed, but ever since then I have had the handles column in Windows Task Manager ena…
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Making Windows Slower Part 2: Process Creation
Windows has long had a reputation for slow file operations and slow process creation. Have you ever wanted to make these operations even slower? This weeks’ blog post covers a technique you can use…
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Localization Failure: Temperature Is Hard
The Guardian is one of my favorite news sources. I’m a subscriber (support news organizations!) and I read it daily. But it is not immune to errors, as this headline shows:68 °F above average is a …
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32 MiB Working Sets on a 64 GiB machine
Memory is a relatively scarce resource on many consumer computers, so a feature to limit how much memory a process uses seems like a good idea, and Microsoft did indeed implement such a feature. Ho…
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Delete an inline function, save 794 kB
In the previous episode of “Simple Changes to Shrink Chrome” I discussed how deleting ‘const’ from a few key locations could lead to dramatic size savings, due to a VC++ com…
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Windows Timer Resolution: Megawatts Wasted
The default timer resolution on Windows is 15.6 ms – a timer interrupt 64 times a second. When programs increase the timer frequency they increase power consumption and harm battery life. They also…
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O(N^2) in CreateProcess
So many possible introductions to this one: Windows 7: Sheesh, I sure am slow at creating processes Windows 10: Hold my beer… Or how about: A) How long does CreateProcess take on Windows? B) How lo…
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What is Windows doing while hogging that lock?
Earlier this month I wrote about how Windows 10 holds a lock during too much of process destruction, which both serializes this task and causes mouse-cursor hitches and UI hangs (because the same l…
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Street address errors in Google Maps
(or actually they do, but they don’t use this knowledge effectively)Update, April 26, 2025: the address fix for W 6th Ave is live, mostly. Going forward I wish that Google Maps would make it harder…
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Add a const here, delete a const there
Update, February 2019: Two years later the VC++ bug I reported here still exists, even in VS 2019 preview. However Chromium no longer builds with VC++ so I’m reverting the changes where I del…