intel_idle: Ignore _CST if control cannot be taken from the platform
e6d4f08a ("intel_idle: Use ACPI _CST on server systems") avoids enabling c-states that have been disabled by the platform with the exception of C1E. Unfortunately, BIOS implementations are not always consistent in terms of how capabilities are advertised and control cannot always be handed over. If control cannot be handed over then intel_idle reports that "ACPI _CST not found or not usable" but does not clear acpi_state_table.count meaning the information is still partially used. This patch ignores ACPI information if CST control cannot be requested from the platform. This was only observed on a number of Haswell platforms that had identical CPUs but not identical BIOS versions. While this problem may be rare overall, 24 separate test cases bisected to this specific commit across 4 separate test machines and is worth addressing. If the situation occurs, the kernel behaves as it did before commit e6d4f08a and uses any c-states that are discovered. The affected test cases were all ones that involved a small number of processes -- exec microbenchmark, pipe microbenchmark, git test suite, netperf, tbench with one client and system call microbenchmark. Each case benefits from being able to use turboboost which is prevented if the lower c-states are unavailable. This may mask real regressions specific to older hardware so it is worth addressing. C-state status before and after the patch 5.9.0-vanilla POLL latency:0 disabled:0 default:enabled 5.9.0-vanilla C1 latency:2 disabled:0 default:enabled 5.9.0-vanilla C1E latency:10 disabled:0 default:enabled 5.9.0-vanilla C3 latency:33 disabled:1 default:disabled 5.9.0-vanilla C6 latency:133 disabled:1 default:disabled 5.9.0-ignore-cst-v1r1 POLL latency:0 disabled:0 default:enabled 5.9.0-ignore-cst-v1r1 C1 latency:2 disabled:0 default:enabled 5.9.0-ignore-cst-v1r1 C1E latency:10 disabled:0 default:enabled 5.9.0-ignore-cst-v1r1 C3 latency:33 disabled:0 default:enabled 5.9.0-ignore-cst-v1r1 C6 latency:133 disabled:0 default:enabled Patch enables C3/C6. Netperf UDP_STREAM netperf-udp 5.5.0 5.9.0 vanilla ignore-cst-v1r1 Hmean send-64 193.41 ( 0.00%) 226.54 * 17.13%* Hmean send-128 392.16 ( 0.00%) 450.54 * 14.89%* Hmean send-256 769.94 ( 0.00%) 881.85 * 14.53%* Hmean send-1024 2994.21 ( 0.00%) 3468.95 * 15.85%* Hmean send-2048 5725.60 ( 0.00%) 6628.99 * 15.78%* Hmean send-3312 8468.36 ( 0.00%) 10288.02 * 21.49%* Hmean send-4096 10135.46 ( 0.00%) 12387.57 * 22.22%* Hmean send-8192 17142.07 ( 0.00%) 19748.11 * 15.20%* Hmean send-16384 28539.71 ( 0.00%) 30084.45 * 5.41%* Fixes: e6d4f08a ("intel_idle: Use ACPI _CST on server systems") Signed-off-by: NMel Gorman <mgorman@techsingularity.net> Cc: 5.6+ <stable@vger.kernel.org> # 5.6+ Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
Showing
想要评论请 注册 或 登录