mainlining shenanigans
9a64c65083
Unfortunately, it seems that the HPD IRQ storm problem from the early days of Intel GPUs was never entirely solved, only mostly. Within the last couple of days, I got a bug report from one of our customers who had been having issues with their machine suddenly booting up very slowly after having updated. The amount of time it took to boot went from around 30 seconds, to over 6 minutes consistently. After some investigation, I discovered that i915 was reporting massive amounts of short HPD IRQ spam on this system from the DisplayPort port, despite there not being anything actually connected. The symptoms would start with one "long" HPD IRQ being detected at boot: [ 1.891398] [drm:intel_get_hpd_pins [i915]] hotplug event received, stat 0x00440000, dig 0x00440000, pins 0x000000a0 [ 1.891436] [drm:intel_hpd_irq_handler [i915]] digital hpd port B - long [ 1.891472] [drm:intel_hpd_irq_handler [i915]] Received HPD interrupt on PIN 5 - cnt: 0 [ 1.891508] [drm:intel_hpd_irq_handler [i915]] digital hpd port D - long [ 1.891544] [drm:intel_hpd_irq_handler [i915]] Received HPD interrupt on PIN 7 - cnt: 0 [ 1.891592] [drm:intel_dp_hpd_pulse [i915]] got hpd irq on port B - long [ 1.891628] [drm:intel_dp_hpd_pulse [i915]] got hpd irq on port D - long … followed by constant short IRQs afterwards: [ 1.895091] [drm:intel_encoder_hotplug [i915]] [CONNECTOR:66:DP-1] status updated from unknown to disconnected [ 1.895129] [drm:i915_hotplug_work_func [i915]] Connector DP-3 (pin 7) received hotplug event. [ 1.895165] [drm:intel_dp_detect [i915]] [CONNECTOR:72:DP-3] [ 1.895275] [drm:intel_get_hpd_pins [i915]] hotplug event received, stat 0x00200000, dig 0x00200000, pins 0x00000080 [ 1.895312] [drm:intel_hpd_irq_handler [i915]] digital hpd port D - short [ 1.895762] [drm:intel_get_hpd_pins [i915]] hotplug event received, stat 0x00200000, dig 0x00200000, pins 0x00000080 [ 1.895799] [drm:intel_hpd_irq_handler [i915]] digital hpd port D - short [ 1.896239] [drm:intel_dp_aux_xfer [i915]] dp_aux_ch timeout status 0x71450085 [ 1.896293] [drm:intel_get_hpd_pins [i915]] hotplug event received, stat 0x00200000, dig 0x00200000, pins 0x00000080 [ 1.896330] [drm:intel_hpd_irq_handler [i915]] digital hpd port D - short [ 1.896781] [drm:intel_get_hpd_pins [i915]] hotplug event received, stat 0x00200000, dig 0x00200000, pins 0x00000080 [ 1.896817] [drm:intel_hpd_irq_handler [i915]] digital hpd port D - short [ 1.897275] [drm:intel_get_hpd_pins [i915]] hotplug event received, stat 0x00200000, dig 0x00200000, pins 0x00000080 The customer's system in question has a GM45 GPU, which is apparently well known for hotplugging storms. So, workaround this impressively broken hardware by changing the default HPD storm threshold from 5 to 50. Then, make long IRQs count for 10, and short IRQs count for 1. This makes it so that 5 long IRQs will trigger an HPD storm, and on systems with short HPD storm detection 50 short IRQs will trigger an HPD storm. 50 short IRQs amounts to 100ms of constant pulsing, which seems like a good middleground between being too sensitive and not being sensitive enough (which would cause visible stutters in userspace every time a storm occurs). And just to be extra safe: we don't enable this by default on systems with MST support. There's too high of a chance of MST support triggering storm detection, and systems that are new enough to support MST are a lot less likely to have issues with IRQ storms anyway. As a note: this patch was tested using a ThinkPad T450s and a Chamelium to simulate the short IRQ storms. Changes since v1: - Don't use two separate thresholds, just make long IRQs count for 10 each and short IRQs count for 1. This simplifies the code a bit - Ville Syrjälä Changes since v2: - Document @long_hpd in intel_hpd_irq_storm_detect, no functional changes Changes since v4: - Remove !! in long_hpd assignment - Ville Syrjälä - queue_hp = true - Ville Syrjälä Signed-off-by: Lyude Paul <lyude@redhat.com> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20181106213017.14563-6-lyude@redhat.com |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.