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It seems that the DMC likes to transition between the DC states a lot when there are no connected displays (no active power domains) during command submission. This activity on DC states has a negative impact on the performance of the chip with huge latencies observed in the interrupt handlers and elsewhere. Simple tests like igt/gem_latency -n 0 are slowed down by a factor of eight. Work around it by introducing a new power domain named, POWER_DOMAIN_GT_IRQ, associtated with the "DC off" power well, which is held for the duration of command submission activity. CNL has the same problem which will be addressed as a follow-up. Doing that requires a fix for a DC6 context corruption problem in the CNL DMC firmware which is yet to be released. v2: * Add commit text as comment in i915_gem_mark_busy. (Chris Wilson) * Protect macro body with braces. (Jani Nikula) v3: * Add dedicated power domain for clarity. (Chris, Imre) * Commit message and comment text updates. * Apply to all big-core GEN9 parts apart for Skylake which is pending DMC firmware release. v4: * Power domain should be inner to device runtime pm. (Chris) * Simplify NEEDS_CSR_GT_PERF_WA macro. (Chris) * Handle async DMC loading by moving the GT_IRQ power domain logic into intel_runtime_pm. (Daniel, Chris) * Include small core GEN9 as well. (Imre) v5 * Special handling for async DMC load is not needed since on failure the power domain reference is kept permanently taken. (Imre) v6: * Drop the NEEDS_CSR_GT_PERF_WA macro since all firmwares have now been deployed. (Imre, Chris) Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100572 Testcase: igt/gem_exec_nop/headless Cc: Imre Deak <imre.deak@intel.com> Acked-by: Chris Wilson <chris@chris-wilson.co.uk> (v2) Cc: Chris Wilson <chris@chris-wilson.co.uk> Cc: Dmitry Rogozhkin <dmitry.v.rogozhkin@intel.com> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> (v5) Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> [Imre: Add note about applying the WA on CNL as a follow-up] Signed-off-by: Imre Deak <imre.deak@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20171205132854.26380-1-tvrtko.ursulin@linux.intel.com
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. 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.