Viewing profile — emmericp

(Native German speaker here), it's a very rare use of the word "free" and usually only used in fixed terms like "Freibier", it wouldn't even work for other drinks, e.g., you can't …

I'm surprised that the recent advances in applying typography to engineering problems [1, 2] are not published at SIGBOVIK but are apparently going to a more serious journal. [1] h…

The time-travelling UB interpretation was popularized by this blog post about 10 years ago [1]. I'm not enough of a specification lawyer to say that this is definitely true, but th…

uIP (TCP/IP stack for tiny microcontrollers) is a another fun real-world example for these types of coroutines: https://github.com/adamdunkels/uip/blob/master/uip/lc-switch...

66% was drivers in 2019.

My aunt donated my grandpa‘s old slide rule there some time ago [0]. Crazy how far we came in just two generations. Fun to see this site show up on HN :) [0] https://sliderulemuseu…

Yes, you should publish it. Don't bother cleaning it up if you don't feel like it. No one will judge you for the code quality. Published terrible code is far better than unpublishe…

We wrote some experimental network drivers in high-level languages a few years ago and Java performed better than expected. Yeah, that's a very special and somewhat odd use case, b…

Most "new tech" is engineering, not science. If you want empiricism try academic papers instead of mailing lists ;) Some numbers: most critical bugs in the Linux kernel are due to …

The real root cause for all that flow director mess and core balancing is that there's a huge disconnect between how the hardware works and what the socket API offers by default. T…

Lesson 1: Never ever reboot multiple Ceph nodes without checking if Ceph is happy between reboots. This failure happened early during boot and this could have been handled with no …

The NIC can hash on IPs and UDP ports just fine, nothing to worry about here. Sure, there's the rare case of a connection moving to a different L3/4 flow identifier causing a cache…

The hardware selection and test setup is questionable, yeah. But downclocking the CPU is pretty standard for many benchmarks like that. Would have been better to evaluate the effec…

Isn't a large part of the performance gain from TSO offloading on transmit due to avoiding working with way too many skb's in the kernel? Shouldn't GSO for UDP with proper NIC supp…

> But enabling tcp timestamps in general case brings little benefit and wastes 12 bytes of each packet for basically no gain. I disagree; TCP timestamps are awesome. Linux enables …

There's only one level of TLBs in the IOMMU. And that's 64 entries. Yeah, I think the dTLB is only 64 entries on Intel CPUs as well, but there's a second larger layer behind that, …

Interesting, did you use huge pages? I think ~100k to 200k TSO "packets" per second should be doable with the IOMMU. But I guess it depends where the data is coming from. Could be …

A problem on the hardware side is that Intel's IOMMU TLB is tiny (64 entries), so using huge pages for all DMA-accessible memory is absolutely required to get a good performance ou…

Related: I ran some benchmarks for all GCs in OpenJDK 12 some time ago: https://github.com/ixy-languages/ixy-languages/blob/master/J... Epsilon tied on speed but lost to Shenandoah…

Not a game developer, but I used to write UI addons for World of Warcraft. WoW allows you to customize your UI heavily with these Lua plugins ("addons") and Lua is garbage collecte…

The Semaphore is only used during initialization, never in the critical path, see profiling results in the main repo

Yes, we do if we want to have an idiomatic interface for the application on top of the driver. Pull requests proving otherwise are welcome

Yes, we could write most of the critical part in C and it would probably be faster. But then it wouldn't be a Swift driver.

Java reaches 52% of C speed in the benchmark game ("fastest measurement at the largest workload" data set, geometric mean), we reach 38%. Seems like our implementation is within a …

PCIe bandwidth also decreases with increasing packet size as there's a lot of overhead per packet. Memory isn't used, it's all handled in cache, hitting main memory is super slow.