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Tue, 7 Jul 2026 22:01:20 +0000 (UTC) Date: Tue, 7 Jul 2026 15:01:16 -0700 From: Borislav Petkov To: Babu Moger Cc: corbet@lwn.net, tony.luck@intel.com, reinette.chatre@intel.com, Dave.Martin@arm.com, james.morse@arm.com, tglx@kernel.org, ben.horgan@arm.com, fenghuay@nvidia.com, skhan@linuxfoundation.org, x86@kernel.org, mingo@redhat.com, dave.hansen@linux.intel.com, hpa@zytor.com, akpm@linux-foundation.org, rdunlap@infradead.org, peterz@infradead.org, feng.tang@linux.alibaba.com, dapeng1.mi@linux.intel.com, elver@google.com, enelsonmoore@gmail.com, kuba@kernel.org, ebiggers@kernel.org, lirongqing@baidu.com, seanjc@google.com, nikunj@amd.com, xin@zytor.com, pawan.kumar.gupta@linux.intel.com, tiala@microsoft.com, chang.seok.bae@intel.com, kprateek.nayak@amd.com, prathyushi.nangia@amd.com, kim.phillips@amd.com, naveen@kernel.org, darwi@linutronix.de, elena.reshetova@intel.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, thomas.lendacky@amd.com, eranian@google.com, peternewman@google.com, qinyuntan@linux.alibaba.com Subject: Re: [RESEND PATCH v4 01/15] x86/resctrl: Support Privilege Level Zero Association (PLZA) Message-ID: <20260707220116.GFak13LChoDbSaCh1O@fat_crate.local> References: Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On Tue, Jul 07, 2026 at 04:50:02PM -0500, Babu Moger wrote: > Customers have identified an issue while using the QoS resource control Please drop the "customers" speak from kernel code. > feature. If memory bandwidth associated with a CLOSID is aggressively > throttled, and a task with that CLOSID moves into kernel mode, the kernel > operations are also aggressively throttled. This can stall forward progress > and eventually degrade overall system performance. > > AMD hardware supports a feature Privilege Level Zero Association (PLZA), > which allows the CPU's CLOSID association to be changed during the > transition from user mode to kernel mode. This allows the kernel to run > using a different CLOSID than user space, which can improve system > performance in certain scenarios. > > The feature is detected via CPUID_Fn80000020_EBX_x00 [Bit 9]: > Privilege Level Zero Association (PLZA). > > The PLZA feature details are documented in [1] available from [2]. > > [1] AMD64 Zen6 Platform Quality of Service (PQOS) Extensions: > Publication # 69193 Revision: 1.00, Issue Date: March 2026 > > Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 # [2] > Signed-off-by: Babu Moger > --- > v4: Split the patch into 2. This patch only handles x86 changes. > Re-wrote the changelog along the ABMC changes. > > v3: Code did not change. Patch order changed. > Added documentation link. > > v2: Rebased on top of the latest tip. > --- > arch/x86/include/asm/cpufeatures.h | 1 + > arch/x86/kernel/cpu/scattered.c | 1 + > 2 files changed, 2 insertions(+) With that addressed: Acked-by: Borislav Petkov (AMD) -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette