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Thu, 14 Aug 2025 01:54:59 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20250806081051.3533470-1-hugoolli@tencent.com> In-Reply-To: From: hugo lee Date: Thu, 14 Aug 2025 16:54:48 +0800 X-Gm-Features: Ac12FXyTwb6Y8hZWBTcTDClMAPIoIb86P0PovYxlG7bfsJ_rcqsHHhAZbSN_pBs Message-ID: Subject: Re: [PATCH] KVM: x86: Synchronize APIC State with QEMU when irqchip=split To: David Woodhouse Cc: Sean Christopherson , pbonzini@redhat.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Yuguo Li Content-Type: text/plain; charset="UTF-8" On Wed, Aug 13, 2025 David Woodhouse wrote: > > On Wed, 2025-08-13 at 17:30 +0800, hugo lee wrote: > > > > Sorry for the misleading, what I was going to say is > > do only cpu_synchroniza_state() in this new userspace exit reason > > and do nothing on the PIT. > > So QEMU will ignore the PIT as the guests do. > > > > The resample is great and needed, but the synchronization > > makes more sense to me on this question. > > So if the guest doesn't actually quiesce the PIT, QEMU will *still* > keep waking up to waggle the PIT output pin, it's just that QEMU won't > bother telling the kernel about it? Yes, just as guests wish. This could eliminate the most performance loss. But I guess resample is more acceptable.