From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yw1-f202.google.com (mail-yw1-f202.google.com [209.85.128.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 338DF4F898 for ; Thu, 11 Jan 2024 15:55:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="Zl7+pKwq" Received: by mail-yw1-f202.google.com with SMTP id 00721157ae682-5efb07ddb0fso79882137b3.0 for ; Thu, 11 Jan 2024 07:55:05 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1704988505; x=1705593305; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=1SJUm7xO3Evzayv5fC2fSXpyvL1vUufTgbZOsh5liOg=; b=Zl7+pKwq2AnSvsPfGc1+z5i3yP+FHpL4gEUCqX1HeoMN/N2RXJjd9FakZeHWIrx02Q Kyrf9wN2awuptcH+LPEbfnFLtKi9BSObdNeUUuH5f4tUCRV7k8yhEilGetlQH4Nk5uCQ lVpqkEZXLO7qYMOKAgxNcY7ZUhZYv0Me0i94yNQxquxN/J4lznpvZueCuwwiR+9B8n44 rdEIV3DanXkaNjQx0qW4bioRWruW6ZYotkVjFtD3Zpyh3+qha0JNtEQYH3xYVL9WpaQz zdvWLwKbyLVE+2sVqTFHryOUsL2bys/jJZQurJzLLxFbWJchZoN/iTMYBVoZbNPSq+tF GX8w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1704988505; x=1705593305; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=1SJUm7xO3Evzayv5fC2fSXpyvL1vUufTgbZOsh5liOg=; b=ll4ubmFLJajHPoY2Hpp7uLCjbUrWw2VZkwuC2cXT8atLj/9QfiPuKH8GYwXsq6Ngya uOn3I5Hkke45jTmdXwHmHXUWK3ws1Mf1VkRZ/iYpPCnYAEm9UuqS+LMWHpxzsiAH6//V YgFYyLO2pc+VdUj17sPHuqq490lYAJUWfLXinvUEj5U1okZAcuw1TBa/ZmPGxJ39ACP6 mrJmeMZvayCX0T6Vn7QxqdrNFAP9Sn1yTsc/A0hlhq02GyhjFOYs4Le0l7yNmt30hYCl wF/4E+nL7STTnMUofeVrxiLUA7Oq0p7ivJ+fvGTsy6E2sT3mhAR5AZFny4y68+pfRWdY Bbbw== X-Gm-Message-State: AOJu0YxH8fxwTN3VpPg6ZDNIeRenYA2CEOX+9nOqlLuDQIVZO9nf6gXb Cby7FeGS66rl6Vx00ZqvUs30Y8ECq0cXurlDfg== X-Google-Smtp-Source: AGHT+IF1xWCjoIQItZuGu9eaJfriQfTcMrLXNiNbqnl8d06y5JDsVMVmQ5EttlPeW+v5bIyKr5TNPgCcIgM= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:690c:3486:b0:5fb:636b:4b4d with SMTP id fo6-20020a05690c348600b005fb636b4b4dmr162765ywb.3.1704988505161; Thu, 11 Jan 2024 07:55:05 -0800 (PST) Date: Thu, 11 Jan 2024 07:55:03 -0800 In-Reply-To: Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: Message-ID: Subject: Re: [Bug 218259] High latency in KVM guests From: Sean Christopherson To: bugzilla-daemon@kernel.org Cc: kvm@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Mon, Dec 18, 2023, bugzilla-daemon@kernel.org wrote: > > I think the kernel is preemptible: > > Ya, not fully preemptible (voluntary only), but the important part is that KVM > will drop mmu_lock if there is contention (which is a "requirement" for the bug > that Yan encountered). For posterity, the above is wrong. Volutary preemption isn't _supposed_ to enable yielding of contended spinlocks/rwlocks, but due to a bug with dynamic preemption, the behavior got enabled for all preempt models: https://lore.kernel.org/all/20240110214723.695930-1-seanjc@google.com