On Wed, 11 Sep 2013 11:16:43 -0400 Peter Hurley <peter@xxxxxxxxxxxxxxxxxx> wrote: > > The funny part is, there's a comment there that shows that this was > > done even for "PREEMPT_RT". Unfortunately, the call to > > "get_scanout_position()" can call functions that use the rt-mutex > > "sleeping spin locks" and it breaks there. > > > > I guess we need to ask the authors of the mainline patch exactly why > > that preempt_disable() is needed? > > The drm core associates a timestamp with each vertical blank frame #. > Drm drivers can optionally support a 'high resolution' hw timestamp. > The vblank frame #/timestamp tuple is user-space visible. > > The i915 drm driver supports a hw timestamp via this drm helper function > which computes the timestamp from the crtc scan position (based on the > pixel clock). > > For mainline, the preempt_disable/_enable() isn't actually necessary > because every call tree that leads here already has preemption disabled. > > For -RT, the maybe i915 register spinlock (uncore.lock) should be raw? > No, it should not. Note, any other lock that can be held when it is held would also need to be raw. And by taking a quick audit of the code, I see this: spin_lock_irqsave(&dev_priv->uncore.lock, irqflags); /* Reset the chip */ /* GEN6_GDRST is not in the gt power well, no need to check * for fifo space for the write or forcewake the chip for * the read */ __raw_i915_write32(dev_priv, GEN6_GDRST, GEN6_GRDOM_FULL); /* Spin waiting for the device to ack the reset request */ ret = wait_for((__raw_i915_read32(dev_priv, GEN6_GDRST) & GEN6_GRDOM_FULL) == 0, 500); That spin is unacceptable in RT with preemption and interrupts disabled. What's the real issue here? Does it have something to do with this dump? [ 3.932060] ------------[ cut here ]------------ [ 3.936809] WARNING: at /home/rostedt/work/git/linux-rt.git/drivers/gpu/drm/i915/i915_drv.c:322 gen6_gt_force_wake_get+0x4d/0x50 [i915]() [ 3.949229] Hardware name: HP Compaq Pro 6300 SFF [ 3.953988] Modules linked in: i915(+) video i2c_algo_bit drm_kms_helper drm i2c_core [ 3.961943] Pid: 220, comm: udevd Not tainted 3.0.89-test-rt117 #117 [ 3.968343] Call Trace: [ 3.970851] [<ffffffff810671bf>] warn_slowpath_common+0x7f/0xc0 [ 3.970852] [<ffffffff8106721a>] warn_slowpath_null+0x1a/0x20 [ 3.970857] [<ffffffffa006569d>] gen6_gt_force_wake_get+0x4d/0x50 [i915] [ 3.970865] [<ffffffffa00962ab>] ivybridge_init_clock_gating+0xcb/0x2f0 [i915] [ 3.970870] [<ffffffffa0090209>] ? intel_crtc_disable+0x29/0x60 [i915] [ 3.970877] [<ffffffffa009f741>] intel_modeset_init+0x751/0x10e0 [i915] [ 3.970882] [<ffffffffa006a158>] i915_driver_load+0xfc8/0x17f0 [i915] [ 3.970885] [<ffffffff8137909e>] ? device_register+0x1e/0x30 [ 3.970892] [<ffffffffa001f596>] ? drm_sysfs_device_add+0x86/0xb0 [drm] [ 3.970896] [<ffffffffa001b8b3>] ? drm_get_minor+0x233/0x300 [drm] [ 3.970900] [<ffffffffa001dd49>] drm_get_pci_dev+0x189/0x2a0 [drm] [ 3.970902] [<ffffffff8105e31b>] ? migrate_enable+0x8b/0x1c0 [ 3.970910] [<ffffffffa00c5f27>] i915_pci_probe+0x1b/0x1d [i915] [ 3.970913] [<ffffffff812c5b6c>] local_pci_probe+0x5c/0xd0 [ 3.970915] [<ffffffff812c73f9>] pci_device_probe+0x109/0x130 [ 3.970917] [<ffffffff8137bc6c>] driver_probe_device+0x9c/0x2b0 [ 3.970918] [<ffffffff8137bf2b>] __driver_attach+0xab/0xb0 [ 3.970919] [<ffffffff8137be80>] ? driver_probe_device+0x2b0/0x2b0 [ 3.970920] [<ffffffff8137be80>] ? driver_probe_device+0x2b0/0x2b0 [ 3.970921] [<ffffffff8137aa34>] bus_for_each_dev+0x64/0xa0 [ 3.970923] [<ffffffff8137b87e>] driver_attach+0x1e/0x20 [ 3.970924] [<ffffffff8137b490>] bus_add_driver+0x1b0/0x290 [ 3.970925] [<ffffffff8137c4a6>] driver_register+0x76/0x140 [ 3.970927] [<ffffffff812c70a2>] __pci_register_driver+0x82/0x100 [ 3.970930] [<ffffffff815b1f6d>] ? notifier_call_chain+0x4d/0x70 [ 3.970934] [<ffffffffa001df7a>] drm_pci_init+0x11a/0x130 [drm] [ 3.970935] [<ffffffffa00f4000>] ? 0xffffffffa00f3fff [ 3.970940] [<ffffffffa00f408b>] i915_init+0x8b/0x8d [i915] [ 3.970943] [<ffffffff81002040>] do_one_initcall+0x40/0x180 [ 3.970946] [<ffffffff810aa4ae>] sys_init_module+0xbe/0x230 [ 3.970948] [<ffffffff815b5a82>] system_call_fastpath+0x16/0x1b [ 3.970949] ---[ end trace 0000000000000002 ]--- [ 4.164458] ------------[ cut here ]------------ -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
