From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> The wbinvd() renders the system with i915 unusable on RT. Using this expensive instruction avoids GPU trouble according to https://bugs.freedesktop.org/show_bug.cgi?id=62191 As a workaround for RT it is recommended to pin each GPU related process to the same CPU and then disable this instruction via the module paramter. Cc: stable-rt@xxxxxxxxxxxxxxx Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> --- drivers/gpu/drm/i915/i915_gem.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index 18da42c..a3f72cb 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -36,6 +36,7 @@ #include <linux/swap.h> #include <linux/pci.h> #include <linux/dma-buf.h> +#include <linux/module.h> static __must_check int i915_gem_object_flush_gpu_write_domain(struct drm_i915_gem_object *obj); static void i915_gem_object_flush_gtt_write_domain(struct drm_i915_gem_object *obj); @@ -2525,6 +2526,10 @@ static inline int fence_number(struct drm_i915_private *dev_priv, return fence - dev_priv->fence_regs; } +static bool do_wbinvd = true; +module_param(do_wbinvd, bool, 0644); +MODULE_PARM_DESC(do_wbinvd, "Do expensive synchronization. Say no after you pin each GPU process to the same CPU in order to lower the latency."); + static void i915_gem_write_fence__ipi(void *data) { wbinvd(); @@ -2548,8 +2553,16 @@ static void i915_gem_object_update_fence(struct drm_i915_gem_object *obj, * on each processor in order to manually flush all memory * transactions before updating the fence register. */ - if (HAS_LLC(obj->base.dev)) - on_each_cpu(i915_gem_write_fence__ipi, NULL, 1); + if (HAS_LLC(obj->base.dev)) { + if (do_wbinvd) { +#ifdef CONFIG_PREEMPT_RT_FULL + pr_err_once("WARNING! The i915 invalidates all caches which increases the latency."); + pr_err_once("As a workaround use 'i915.do_wbinvd=no' and PIN each process doing "); + pr_err_once("any kind of GPU activity to the same CPU to avoid problems."); +#endif + on_each_cpu(i915_gem_write_fence__ipi, NULL, 1); + } + } i915_gem_write_fence(dev, fence_reg, enable ? obj : NULL); if (enable) { -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe stable-rt" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
