From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6651A2F39B4; Thu, 14 Aug 2025 09:10:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755162661; cv=none; b=o7D9nTsUU5zJwIUopvAyZBC94mwhslFb7OsIebhx0aMI05WlfpLqx2D0odLHBtAnKAZD4+cvR1H7li1WeWrCfiqW6hccKhsk3XwB/HeW9/XJuNiQUMtV0RPAys7O2pAFcWuazN/vAoEGKOsvBafCsPUOfgblecLFQM/4FiSlt3A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755162661; c=relaxed/simple; bh=y1lZ3kLM+nN4UUsPXSJwemJmkst+TnOf2pZlX2u6AbI=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=CE84EObENmlmwkTh5QR99cxo1qyyxMG8GM+/OPYMDuDtkWxyMrPUOSz9NdhaKTSTcec4OL5nz8NQGVpfLqXyny/XsMi0fGBcCpLFB03BOpcH92jUmcZtqy9362i5efx7hnOKnUU+NSdF2nBOKVCmGInSnu3tobrmtlw8+05FqBA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=casper.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=Ur9gmb3U; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=casper.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Ur9gmb3U" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=y1lZ3kLM+nN4UUsPXSJwemJmkst+TnOf2pZlX2u6AbI=; b=Ur9gmb3UvSFaZLiDWxPI5zMxj/ Ey62Xeq3G0Xi2sSMlnoJlybFUe2BXtmqQNDzVVaGjYUIG0TFisyUITDQo40FLFIRuvF8alGqW0KNC b2M/bNlE/lglkvLiiqWVgnXVNsHdi5dTjBPL9qqcoH9RmQRHhQZLdYO+A1wg5c23fU8dEAy//a/q7 PH/BVN3HVYdOl2BjWoTRmYf6Vu2eoV2jrKO3Etqt21g4vU4z3CEvJVlweHgDBFH5L3uieUjMAQnuD 3+ggH8h/AU3MYGGduxDO/g4kot/cPn8plcEtNfmKw5tIN2g7UheqGLJu8AhSndKn1LDR+3p9uZYrN OQaMNbtQ==; Received: from [54.239.6.185] (helo=u09cd745991455d.ant.amazon.com) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1umTym-0000000GdJm-2Nn5; Thu, 14 Aug 2025 09:10:37 +0000 Message-ID: <193779d766e08f4e013326da9f1de9de5e030398.camel@infradead.org> Subject: Re: [PATCH] KVM: x86: Synchronize APIC State with QEMU when irqchip=split From: David Woodhouse To: hugo lee 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 Date: Thu, 14 Aug 2025 11:10:35 +0200 In-Reply-To: References: <20250806081051.3533470-1-hugoolli@tencent.com> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-g8cy2fLh8ofIckiPZit+" User-Agent: Evolution 3.52.3-0ubuntu1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html --=-g8cy2fLh8ofIckiPZit+ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2025-08-14 at 16:54 +0800, hugo lee wrote: > On Wed, Aug 13, 2025 David Woodhouse wrote: > >=20 > > On Wed, 2025-08-13 at 17:30 +0800, hugo lee wrote: > > >=20 > > > 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. > > >=20 > > > The resample is great and needed, but the synchronization > > > makes more sense to me on this question. > >=20 > > 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? >=20 > Yes, just as guests wish. > This could eliminate the most performance loss. >=20 > But I guess resample is more acceptable. Simpler, cleaner, solves it for more use cases including when the interrupt *is* delivered to the PIC but just never services. And allows us to fix the VFIO INTx abomination and use the kernel's irqfd API properly... But that's a discussion for the qemu-devel list, I suppose. --=-g8cy2fLh8ofIckiPZit+ Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCD9Aw ggSOMIIDdqADAgECAhAOmiw0ECVD4cWj5DqVrT9PMA0GCSqGSIb3DQEBCwUAMGUxCzAJBgNVBAYT AlVTMRUwEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5jb20xJDAi BgNVBAMTG0RpZ2lDZXJ0IEFzc3VyZWQgSUQgUm9vdCBDQTAeFw0yNDAxMzAwMDAwMDBaFw0zMTEx MDkyMzU5NTlaMEExCzAJBgNVBAYTAkFVMRAwDgYDVQQKEwdWZXJva2V5MSAwHgYDVQQDExdWZXJv a2V5IFNlY3VyZSBFbWFpbCBHMjCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMjvgLKj jfhCFqxYyRiW8g3cNFAvltDbK5AzcOaR7yVzVGadr4YcCVxjKrEJOgi7WEOH8rUgCNB5cTD8N/Et GfZI+LGqSv0YtNa54T9D1AWJy08ZKkWvfGGIXN9UFAPMJ6OLLH/UUEgFa+7KlrEvMUupDFGnnR06 aDJAwtycb8yXtILj+TvfhLFhafxroXrflspavejQkEiHjNjtHnwbZ+o43g0/yxjwnarGI3kgcak7 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