Messages in this thread | | | Date | Fri, 14 Oct 2022 15:17:03 -0300 | Subject | Re: [PATCH V2] x86/split_lock: Add sysctl to control the misery mode | From | André Almeida <> |
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Hi Guilherme,
On 10/14/22 15:05, Guilherme G. Piccoli wrote: > Commit b041b525dab9 ("x86/split_lock: Make life miserable for split lockers") > changed the way the split lock detector works when in "warn" mode; > basically, not only it shows the warn message, but also intentionally > introduces a slowdown (through sleeping plus serialization mechanism) > on such task. Based on discussions in [0], seems the warning alone > wasn't enough motivation for userspace developers to fix their > applications. > > Happens that originally the proposal in [0] was to add a new mode > which would warns + slowdown the "split locking" task, keeping the > old warn mode untouched. In the end, that idea was discarded and > the regular/default "warn" mode now slowdowns the applications. This > is quite aggressive with regards proprietary/legacy programs that > basically are unable to properly run in kernel with this change. > While is understandable that a malicious application could try a DoS > by split locking, it seems unacceptable to regress old/proprietary > userspace programs through a default configuration that previously > worked. An example of such breakage was reported in [1]. > > So let's add a sysctl to allow controlling the "misery mode" behavior, > as per Thomas suggestion on [2]. This way, users running legacy and/or > proprietary software are allowed to still execute them with a decent > performance while still observe the warning messages on kernel log. > > [0] https://lore.kernel.org/lkml/20220217012721.9694-1-tony.luck@intel.com/ > > [1] https://github.com/doitsujin/dxvk/issues/2938 > > [2] https://lore.kernel.org/lkml/87pmf4bter.ffs@tglx/ > > Fixes: b041b525dab9 ("x86/split_lock: Make life miserable for split lockers") > Cc: Andre Almeida <andrealmeid@igalia.com> > Cc: Fenghua Yu <fenghua.yu@intel.com> > Cc: Joshua Ashton <joshua@froggi.es> > Cc: Melissa Wen <mwen@igalia.com> > Cc: Paul Gofman <pgofman@codeweavers.com> > Cc: Pavel Machek <pavel@denx.de> > Cc: Pierre-Loup Griffais <pgriffais@valvesoftware.com> > Cc: Tony Luck <tony.luck@intel.com> > Cc: Zebediah Figura <zfigura@codeweavers.com> > Suggested-by: Thomas Gleixner <tglx@linutronix.de> > Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Tested-by: André Almeida <andrealmeid@igalia.com>
Tested on an Intel i7-1165G7 using a small benchmarking script, the behavior is effectively reverted when using the sysctl option.
Also, you might want to document this option somewhere? Maybe at Documentation/admin-guide/sysctl/kernel.rst
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