Srinivas Pandruvada <srinivas.pandruv...@linux.intel.com> writes: > On Fri, 2018-07-27 at 22:34 -0700, Francisco Jerez wrote: >> Srinivas Pandruvada <srinivas.pandruv...@linux.intel.com> writes: >> >> > Enable HWP boost on Skylake server and workstations. >> > >> >> Please revert this series, it led to significant energy usage and >> graphics performance regressions [1]. > Which SKX platform is targeted to graphics? >
See the bug report, it's a regular desktop SKL. >> The reasons are roughly the ones >> we discussed by e-mail off-list last April: This causes the >> intel_pstate >> driver to decrease the EPP to zero > No. You didn't check this series. We are not using EPP at all. > The boost mechanism used here is not boost to max. > I see you've changed the mechanism to obtain a latency boost since our last discussion, but that doesn't address my concerns in any way: This series causes the intel_pstate driver to clamp the CPU frequency above the optimal frequency to run the workload at, as a response to the application waiting on IO frequently, even though that's only a sign of the application being IO-bound and *not* a sign of it being latency-sensitive, since the application's IO and CPU work are properly pipelined. This leads to a decrease in parallelism due to the active CPU core using a larger fraction of the package TDP in order to achieve the same work, leading to a decrease in system performance. > Thanks, > Srinivas > >> when the workload blocks on IO >> frequently enough, which for the regressing benchmarks detailed in >> [1] >> is a symptom of the workload being heavily IO-bound, which means they >> won't benefit at all from the EPP boost since they aren't >> significantly >> CPU-bound, and they will suffer a decrease in parallelism due to the >> active CPU core using a larger fraction of the TDP in order to >> achieve >> the same work, causing the GPU to have a lower power budget >> available, >> leading to a decrease in system performance. >> >> You may want to give a shot to my previous suggestion of using [2] in >> order to detect whether the system is IO-bound, which you can use as >> an >> indicator that the optimization implemented in this series cannot >> possibly improve performance and can be expected to hurt energy >> usage. >> >> Thanks. >> >> [1] https://bugs.freedesktop.org/show_bug.cgi?id=107410 >> [2] https://patchwork.kernel.org/patch/10312259/ >> >> > Reported-by: Mel Gorman <mgor...@techsingularity.net> >> > Tested-by: Giovanni Gherdovich <ggherdov...@suse.cz> >> > Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel >> > .com> >> > --- >> > drivers/cpufreq/intel_pstate.c | 10 ++++++++++ >> > 1 file changed, 10 insertions(+) >> > >> > diff --git a/drivers/cpufreq/intel_pstate.c >> > b/drivers/cpufreq/intel_pstate.c >> > index 70bf63bb4e0e..01c8da1f99db 100644 >> > --- a/drivers/cpufreq/intel_pstate.c >> > +++ b/drivers/cpufreq/intel_pstate.c >> > @@ -1794,6 +1794,12 @@ static const struct x86_cpu_id >> > intel_pstate_cpu_ee_disable_ids[] = { >> > {} >> > }; >> > >> > +static const struct x86_cpu_id intel_pstate_hwp_boost_ids[] >> > __initconst = { >> > + ICPU(INTEL_FAM6_SKYLAKE_X, core_funcs), >> > + ICPU(INTEL_FAM6_SKYLAKE_DESKTOP, core_funcs), >> > + {} >> > +}; >> > + >> > static int intel_pstate_init_cpu(unsigned int cpunum) >> > { >> > struct cpudata *cpu; >> > @@ -1824,6 +1830,10 @@ static int intel_pstate_init_cpu(unsigned >> > int cpunum) >> > intel_pstate_disable_ee(cpunum); >> > >> > intel_pstate_hwp_enable(cpu); >> > + >> > + id = x86_match_cpu(intel_pstate_hwp_boost_ids); >> > + if (id) >> > + hwp_boost = true; >> > } >> > >> > intel_pstate_get_cpu_pstates(cpu); >> > -- >> > 2.13.6
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