Evolution of the x86 context switch in Linux (2018)

Can someone say why is using the TSS still mandatory with software-based task switching? Is this a requirement imposed by x86?<p>In looking at the OS dev wiki I see the following:<p>&gt;&quot;The TSS is primarily suited for hardware multitasking, where each individual process has its own TSS. In Software multitasking, one or two TSS&#x27;s are also generally used, as they allow for entering Ring 0 code after an interrupt.&quot;<p>Would you not be able to enter Ring0 after an interrupt with a TSS entry? Is this why it is still required?

I recall reading a paper comparing Linux and Solaris context switch times in ~98 and Linux was 10-100X faster. Solaris did something incredibly slow and safe.

Enjoyed this article, anybody know the significance of adding the do..while(0) loop within the macro starting Linux 1.3?<p>Was curious if it guards against some C pre-processor issues.<p><pre><code> &#x2F;** include&#x2F;asm-i386&#x2F;system.h *&#x2F; #define switch_to(tsk) do { [...] } while (0)</code></pre>

An addition to &quot;Linux 2.2 (1999)&quot; is: introduced meltdown vulnerability. That was the then-unknown cost of software context switching.<p>Later, with Red Hat&#x27;s 4g4g kernels that Linus rejected, the problem would go away for people who installed Red Hat&#x27;s version of the OS on systems with many gigabytes of memory.

Nice article!<p>If you want to have lots of fun, you could look at switch_mm() on a modern kernel :)

This is really well done, bravo.

Very thorough. Nice job.

anyone knows what Ingo Molnar is doing these days?

I really like how good the article looks when printed. I enjoy reading long, in-depth articles much more when I can read them in print. Unfortunately many blog posts need a lot of tweaking until I can get an acceptable print result. This one looks good enough without any trickery.<p>Thanks to the author, for caring about the paper people. : )