Mirror, Mirror on the Wall

[$] Calibrating your fear of big bad optimizing compilers

Fri Oct 11 14:14:00 2019
lwn.net

As noted earlier, when compiling Linux-kernel code that does a plain C-language load or store, as in "a=b", the C standard grants the compiler the right to assume that the affected variables are neither accessed nor modified by any other thread at the time of that load or store. The compiler is therefore permitted to carry out a surprisingly large number of optimizations, any number of which might ruin your concurrent code's day. Given that current compilers usually do not emit diagnostics warning of potential ruined days, it would be good to have other tools take on this task.

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Security updates for Friday

Fri Oct 11 14:04:00 2019
lwn.net

Security updates have been issued by Debian (lucene-solr and ruby-openid), Fedora (krb5 and SDL2), openSUSE (kernel and libopenmpt), and Ubuntu (python2.7, python3.4).

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Understanding Scheduling Behavior with SchedViz (Google Open Source Blog)

Thu Oct 10 22:38:00 2019
lwn.net

The Google Open Source Blog has an announcement of the release of the SchedViz tool that is used internally at the company "to discover many opportunities for better scheduling choices and to root-cause many latency issues". SchedViz provides a GUI to explore kernel traces: "The SchedViz UI displays collections in several ways. A zoomable and pannable heatmap shows system cores on the y-axis, and the trace duration on the x-axis. Each core in the system has a swim-lane, and each swim-lane shows CPU utilization (when that CPU is being kept busy) and wait-queue depth (how many threads are waiting to run on that CPU.) The UI also includes a thread list that displays which threads were active in the heatmap, along with how long they ran, waited to run, and blocked on some event, and how many times they woke up or migrated between cores. Individual threads can be selected to show their behavior over time, or expanded to see their details."

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[$] BPF at Facebook (and beyond)

Thu Oct 10 16:47:00 2019
lwn.net

It is no secret that much of the work on the in-kernel BPF virtual machine and associated user-space support code is being done at Facebook. But less is known about how Facebook is actually using BPF. At Kernel Recipes 2019, BPF developer Alexei Starovoitov described a bit of that work, though even he admitted that he didn't know what most of the BPF programs running there were doing. He also summarized recent developments with BPF and some near-future work.

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Security updates for Thursday

Thu Oct 10 13:47:00 2019
lwn.net

Security updates have been issued by Debian (clamav, libtomcrypt, and rsyslog), Fedora (suricata), SUSE (libopenmpt and python-requests), and Ubuntu (libsoup2.4 and octavia).

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[$] An update on the input stack

Wed Oct 9 21:59:00 2019
lwn.net

The input stack for Linux is an essential part of interacting with our systems, but it is also an area that is lacking in terms of developers. There has been progress over the last few years, however; Peter Hutterer from Red Hat came to the 2019 X.Org Developers Conference to talk about some of the work that has been done. He gave a status report on the input stack that covered development work that is going on now as well as things that have been completed in the last two years or so. Overall, things are looking pretty good for input on Linux, though the "bus factor" for the stack is alarmingly low.

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Stallman: No radical changes in GNU Project

Wed Oct 9 18:46:00 2019
lwn.net

Richard Stallman has issued a brief statement saying that there will not be any radical changes in the GNU Project's goals, principles and policies. "I would like to make incremental changes in how some decisions are made, because I won't be here forever and we need to ready others to make GNU Project decisions when I can no longer do so. But these won't lead to unbounded or radical changes."

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