> -----Original Message----- > From: Jack Allister <jalliste@xxxxxxxxxx> > Sent: 04 January 2024 09:06 > Cc: Allister, Jack <jalliste@xxxxxxxxxxxx>; Rafael J . Wysocki > <rafael@xxxxxxxxxx>; Durrant, Paul <pdurrant@xxxxxxxxxxxx>; Wang, Jue > <juew@xxxxxxxxxx>; Usama Arif <usama.arif@xxxxxxxxxxxxx>; Jonathan Corbet > <corbet@xxxxxxx>; Thomas Gleixner <tglx@xxxxxxxxxxxxx>; Ingo Molnar > <mingo@xxxxxxxxxx>; Borislav Petkov <bp@xxxxxxxxx>; Dave Hansen > <dave.hansen@xxxxxxxxxxxxxxx>; x86@xxxxxxxxxx; H. Peter Anvin > <hpa@xxxxxxxxx>; Paul E. McKenney <paulmck@xxxxxxxxxx>; Randy Dunlap > <rdunlap@xxxxxxxxxxxxx>; Tejun Heo <tj@xxxxxxxxxx>; Peter Zijlstra > <peterz@xxxxxxxxxxxxx>; Yan-Jie Wang <yanjiewtw@xxxxxxxxx>; Hans de Goede > <hdegoede@xxxxxxxxxx>; linux-doc@xxxxxxxxxxxxxxx; linux- > kernel@xxxxxxxxxxxxxxx > Subject: [PATCH v6] x86: intel_epb: Add earlyparam option to keep bias at > performance > > Buggy BIOSes may not set a sane boot-time Energy Performance Bias (EPB). > A result of this may be overheating or excess power usage. The kernel > overrides any boot-time EPB "performance" bias to "normal" to avoid this. > > When used in data centers it is preferable keep the EPB at "performance" > when performing a live-update of the host kernel via a kexec to the new > kernel. This is due to boot-time being critical when performing the kexec > as running guest VMs will perceieve this as latency or downtime. > > On Intel Xeon Ice Lake platforms it has been observed that a combination > of > EPB being set to "normal" alongside HWP (Intel Hardware P-states) being > enabled/configured during or close to the kexec causes an increases the > live-update/kexec downtime by 7 times compared to when the EPB is set to > "performance". > > Introduce a command-line parameter, "intel_epb=preserve", to skip the > "performance" -> "normal" override/workaround. This maintains prior > functionality when no parameter is set, but adds in the ability to stay at > performance for a speedy kexec if a user wishes. > > Signed-off-by: Jack Allister <jalliste@xxxxxxxxxx> > Acked-by: Rafael J. Wysocki <rafael@xxxxxxxxxx> > Cc: Paul Durrant <pdurrant@xxxxxxxxxx> > Cc: Jue Wang <juew@xxxxxxxxxx> > Cc: Usama Arif <usama.arif@xxxxxxxxxxxxx> > --- > .../admin-guide/kernel-parameters.txt | 9 ++++++++ > arch/x86/kernel/cpu/intel_epb.c | 22 +++++++++++++++++-- > 2 files changed, 29 insertions(+), 2 deletions(-) > Reviewed-by: Paul Durrant <pdurrant@xxxxxxxxxx>
