[lkml]   [2020]   [Sep]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends
On Thu, Sep 24, 2020 at 08:32:41AM -0400, Steven Rostedt wrote:
> Anyway, instead of blocking. What about having a counter of number of
> migrate disabled tasks per cpu, and when taking a migrate_disable(), and there's
> already another task with migrate_disabled() set, and the current task has
> an affinity greater than 1, it tries to migrate to another CPU?

That doesn't solve the problem. On wakeup we should already prefer an
idle CPU over one running a (RT) task, but you can always wake more
tasks than there's CPUs around and you'll _have_ to stack at some point.

The trick is how to unstack them correctly. We need to detect when a
migrate_disable() task _should_ start running again, and migrate away
whoever is in the way at that point.

It turns out, that getting selected for pull-balance is exactly that
condition, and clearly a migrate_disable() task cannot be pulled, but we
can use that signal to try and pull away the running task that's in the

 \ /
  Last update: 2020-09-24 14:45    [W:0.105 / U:0.876 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site