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Tue, 14 Feb 2023 16:49:51 +0000 Date: Tue, 14 Feb 2023 16:49:51 +0000 Message-ID: <86zg9gxkcw.wl-maz@kernel.org> From: Marc Zyngier To: Usama Arif Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-doc@vger.kernel.org, virtualization@lists.linux-foundation.org, linux@armlinux.org.uk, yezengruan@huawei.com, catalin.marinas@arm.com, will@kernel.org, steven.price@arm.com, mark.rutland@arm.com, bagasdotme@gmail.com, pbonzini@redhat.com, fam.zheng@bytedance.com, liangma@liangbit.com, punit.agrawal@bytedance.com Subject: Re: [v3 0/6] KVM: arm64: implement vcpu_is_preempted check In-Reply-To: <5976b0c9-d4e7-7561-6ce0-790e2460d1ef@bytedance.com> References: <20230117102930.1053337-1-usama.arif@bytedance.com> <5976b0c9-d4e7-7561-6ce0-790e2460d1ef@bytedance.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/28.2 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: usama.arif@bytedance.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-doc@vger.kernel.org, virtualization@lists.linux-foundation.org, linux@armlinux.org.uk, yezengruan@huawei.com, catalin.marinas@arm.com, will@kernel.org, steven.price@arm.com, mark.rutland@arm.com, bagasdotme@gmail.com, pbonzini@redhat.com, fam.zheng@bytedance.com, liangma@liangbit.com, punit.agrawal@bytedance.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230214_084957_047306_48565185 X-CRM114-Status: GOOD ( 22.99 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, 14 Feb 2023 16:06:26 +0000, Usama Arif wrote: > > > > On 17/01/2023 10:29, Usama Arif wrote: > > This patchset adds support for vcpu_is_preempted in arm64, which allows the guest > > to check if a vcpu was scheduled out, which is useful to know incase it was > > holding a lock. vcpu_is_preempted is well integrated in core kernel code and can > > be used to improve performance in locking (owner_on_cpu usage in mutex_spin_on_owner, > > mutex_can_spin_on_owner, rtmutex_spin_on_owner and osq_lock) and scheduling > > (available_idle_cpu which is used in several places in kernel/sched/fair.c > > for e.g. in wake_affine to determine which CPU can run soonest). > > > > This patchset shows significant improvement on overcommitted hosts (vCPUs > pCPUS), > > as waiting for preempted vCPUs reduces performance. > > > > Hi, > > Just wanted to check if there are any comments for this? Not a lot, I'm afraid. My concerns with this thing are still the same: - it is KVM-specific - it doesn't work with nested virtualisation - its correctness is unproven on arm64 I'm also not going to entertain any of this without the core arm64 maintainers saying that they will enable this. Thanks, M. -- Without deviation from the norm, progress is not possible. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel