Kernel and Graphics: Linux I/O Schedulers, Btrfs, Intel, Mesa 18.3.1 and More
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Linux I/O Schedulers
The Linux kernel I/O schedulers attempt to balance the need to get the best possible I/O performance while also trying to ensure the I/O requests are "fairly" shared among the I/O consumers. There are several I/O schedulers in Linux, each try to solve the I/O scheduling issues using different mechanisms/heuristics and each has their own set of strengths and weaknesses.
For traditional spinning media it makes sense to try and order I/O operations so that they are close together to reduce read/write head movement and hence decrease latency. However, this reordering means that some I/O requests may get delayed, and the usual solution is to schedule these delayed requests after a specific time. Faster non-volatile memory devices can generally handle random I/O requests very easily and hence do not require reordering.
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Btrfs Restoring Support For Swap Files With Linux 4.21
The Btrfs file-system hasn't supported Swap files on it in early a decade, but that support will be restored again with the upcoming Linux 4.21 kernel.
Btrfs hasn't supported Swap files on it since 2009 thus making swap partitions necessary unless having a mix of file-systems on your box (or not caring about any swap capabilities), but now with Linux 4.21 that support will be restored for allowing swap files to be reside on Btrfs.
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Intel's IWD Linux Wireless Daemon 0.13 Adds Opportunistic Wireless Encryption
Intel's promising IWD open-source wireless daemon continues picking up additional functionality in its trek towards potentially replacing wpa_supplicant. Out this week is IWD 0.13.
With the IWD 0.13 release there are fixes as well as support for Opportunistic Wireless Encryption and support for the common EAP-TLS framework.
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Intel Developing "oneAPI" For Optimized Code Across CPUs, GPUs, FPGAs & More
Intel's 2018 Architecture Day was primarily focused on the company's hardware architecture road-map, but one of the software (pre)announcements was their oneAPI software stack.
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Intel Working On Open-Sourcing The FSP - Would Be Huge Win For Coreboot & Security
Intel's Architecture Day on Tuesday was delightfully filled with an overwhelming amount of valuable hardware information, but Intel's software efforts were also briefly touched on too. In fact, Raja Koduri reinforced how software is a big part of Intel technology and goes in-hand with their security, interconnect, memory, architecture, and process pillars and that's where their new oneAPI initiative will fit in. But what learning afterwards was most exciting on the software front.
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Linux Is Already In Good Shape For The New Features Of Intel Gen11 Graphics & Icelake
Besides seeing Icelake demos at the Intel Architecture Day that were running on Ubuntu, with closely tracking the Linux kernel's development most of the new features presented for Sunny Cove and Gen11 graphics have already been merged or at least available in patch form for some months within the Linux ecosystem. Here's a look at the features talked about yesterday and their state on Linux.
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Intel Details Gen11 Graphics & Sunny Cove For Icelake
At Intel's architecture day, the company finally detailed their "Gen 11" graphics that we've been seeing open-source Linux graphics driver patches for many months (Intel OTC posted their initial open-source display driver code in early January and has continued the enablement work since) albeit elusive in substantive user details and hardware until Icelake. But today at least we can share more about the significant improvements with Gen11 graphics.
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mesa 18.3.1
This version disables the VK_EXT_pci_bus_info extension due to last minute issues spotted in the specification.
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Mesa 18.3.1 Released To Disable Botched Vulkan Extension
Mesa 18.3 was released less than a week ago while today Mesa 18.3.1 was issued due to an error in the Vulkan specification.
The motivating factor for this quick Mesa 18.3.1 release was to disable the VK_EXT_pci_bus_info extension that had just been introduced weeks ago. The Vulkan working group mistakenly assumed that PCI domains are 16-bit even though they could potentially be 32-bit values. The next Vulkan spec update will change the relevant structure to be 32-bit, which is a backwards-incompatible change.
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High resolution wheel scrolling on Linux v4.21
Most wheel mice have a physical feature to stop the wheel from spinning freely. That feature is called detents, notches, wheel clicks, stops, or something like that. On your average mouse that is 24 wheel clicks per full rotation, resulting in the wheel rotating by 15 degrees before its motion is arrested. On some other mice that angle is 18 degrees, so you get 20 clicks per full rotation.
Of course, the world wouldn't be complete without fancy hardware features. Over the last 10 or so years devices have added free-wheeling scroll wheels or scroll wheels without distinct stops. In many cases wheel behaviour can be configured on the device, e.g. with Logitech's HID++ protocol. A few weeks back, Harry Cutts from the chromium team sent patches to enable Logitech high-resolution wheel scrolling in the kernel. Succinctly, these patches added another axis next to the existing REL_WHEEL named REL_WHEEL_HI_RES. Where available, the latter axis would provide finer-grained scroll information than the click-by-click REL_WHEEL. At the same time I accidentally stumbled across the documentation for the HID Resolution Multiplier Feature. A few patch revisions later and we now have everything queued up for v4.21. Below is a summary of the new behaviour.
The kernel will continue to provide REL_WHEEL as axis for "wheel clicks", just as before. This axis provides the logical wheel clicks, (almost) nothing changes here. In addition, a REL_WHEEL_HI_RES axis is available which allows for finer-grained resolution. On this axis, the magic value 120 represents one logical traditional wheel click but a device may send a fraction of 120 for a smaller motion. Userspace can either accumulate the values until it hits a full 120 for one wheel click or it can scroll by a few pixels on each event for a smoother experience. The same principle is applied to REL_HWHEEL and REL_HWHEEL_HI_RES for horizontal scroll wheels (which these days is just tilting the wheel). The REL_WHEEL axis is now emulated by the kernel and simply sent out whenever we have accumulated 120.
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Nouveau Lands Initial Open-Source NVIDIA Turing Support - But No GPU Acceleration
Just in time for the upcoming Linux 4.21 kernel, the developers working on the reverse-engineered, open-source support for NVIDIA GeForce RTX "Turing" GPUs have published their preliminary code. But before getting too excited, there isn't GPU hardware acceleration working yet.
Ben Skeggs of Red Hat spearheaded this enablement work. He's got the initial support working right now for the TU104 and TU106 chipsets, but not yet TU102 due to hardware access. The TU106 is the RTX 2060/2070 series while the TU104 is the GeForce RTX 2080 and the TU102 is the RTX 2080 Ti and TITAN RTX. Back on launch day the Nouveau community crew started their Turing reverse-engineering work. NVIDIA doesn't support nor hinder the Nouveau driver work, though these days do sample hardware to the developers and are occasionally able to answer technical questions for them.
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