From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f74.google.com (mail-pj1-f74.google.com [209.85.216.74]) (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 8C91BAD21 for ; Fri, 15 Aug 2025 19:28:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.74 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755286086; cv=none; b=mpLUpIUXH/V+SHJHFP4crOtDI5H8GaQIkqiYCzg7bnn2R3hEPazrQoJZI8Ejr2vd+dXFsmZiXQX06UREr6QBpKcME/X2YVv24WVDq9t/CI8vbfr3ym33JCOaNhkySWeIJXXPW7K2xXfONW6WjZYlzBXwr3ARcc9yK6yzBZg4kwA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755286086; c=relaxed/simple; bh=03ai3+jPXw+qIgPjJjhYeat8FHaMCcAxTtMV6J8Fauw=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=DJYNpUN88weBz+L/uxNRcykZsdi398ELnDjtTrjbnYH0ssPsHiu8xfZkXUQHPr9zSlWYxDnXtEpKbQO7tpy9LEIRqo55K2STt9gHe4QG6p7Wca2sulFeWglmze5pywx7lW26leDZ9rm6Gt8+gOvH4umcOBFXqUT09c5l9O7WLCg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=ujw8AG/E; arc=none smtp.client-ip=209.85.216.74 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="ujw8AG/E" Received: by mail-pj1-f74.google.com with SMTP id 98e67ed59e1d1-32326bd712cso2125299a91.2 for ; Fri, 15 Aug 2025 12:28:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1755286085; x=1755890885; 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=CtxMP1qLySSUVXufrp6NxftESi55Z9nJ+C2xCceAidg=; b=ujw8AG/EyBE6stXLKMTbm3ehnQ3ocfhmgWd3ZJRIh2n/xHq6eVan/HhZnu/rEOHn/f 1hbzBAa8BPYmYo98FgkWBN5EYsmsg2Uixs1mbz9y3KbjnD2lrxoTbg3zJeP4C/YlzOKw 631IfSgOnBF3sBN7xIt0hWySpCG/ipacwYiiOH/E+D42Ec3PNck5PKd7Bs4WJYko4fxx DpotTIWxgYs8TM3HuBVagv2uc/GvoWF65QkpeFRQHtMvU0ey+/fM29bAA8dYnk4wfgda r9rWS8KCSNiua3Bx92LJ+bYmaPRKoUizzWNceGjUXK792P4dp6xVdBjRu0Ps+83ZAmyO 0mRg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1755286085; x=1755890885; 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=CtxMP1qLySSUVXufrp6NxftESi55Z9nJ+C2xCceAidg=; b=hfPcpRRZHC52lD914v8B8NoVDaqhyyre6wrbvLX2Z7YXMvid1Z/4lpQMRek5oPZ4oF bF1CsMgodv2LOX84ULuKtpA2O26TlqZrKeNC2M5JwoPumG88BUqf7jvAfwftG1MqQ+0+ Ti1A6CZnfYKeB2DAz6hZidNfEot9B1gfiR6wgT2zdj1DCoEmERB/JsHqVl4hPv7OOP9k BoYrMRdp2KogtYs794QoRK+O6EU0ZANS3TZ2abbbpchKTrRH1Tw4Ka10K/iwxSd9S+bG lK5AEOGTeyymfgDoD4XrYe/pgGsVOUWiTWe/TBqIAmxOa4+ez94rCVaSTw7x54xsjMYm tTxw== X-Forwarded-Encrypted: i=1; AJvYcCWiPQ8BvlYlwa0E1HlvEhKMghbA4UnHHHSEQRdg2kbcYQ6XNqvAjqEK7DFev7jAjgBMlvk=@vger.kernel.org X-Gm-Message-State: AOJu0YxiBrLiSm4ClW2VmmRmtYrbk5mpAzcCFwdPaMNaQL+lMkMSCROP KpFRkgJlVk61Ou4oWBFB4t4f1XPqRhBv+aqW9qpUKc9phnWHnsA2Q7KVjsnQw1yolIhvzhC1vwX Tbu0MDA== X-Google-Smtp-Source: AGHT+IFheb7H3vGWMwDpPa/ZTz43jwwEwav9YvOcV9yuk5MWwK/8m1Y/ywXNiBd1O4MgZl8Zxb99lnXh3Wc= X-Received: from pjbph13.prod.google.com ([2002:a17:90b:3bcd:b0:31f:232:1fae]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:4b10:b0:30a:4874:5397 with SMTP id 98e67ed59e1d1-32341ebf8bemr4526630a91.9.1755286084895; Fri, 15 Aug 2025 12:28:04 -0700 (PDT) Date: Fri, 15 Aug 2025 12:28:03 -0700 In-Reply-To: <20250722110005.4988-1-lirongqing@baidu.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250722110005.4988-1-lirongqing@baidu.com> Message-ID: Subject: Re: [PATCH][v2] x86/kvm: Prefer native qspinlock for dedicated vCPUs irrespective of PV_UNHALT From: Sean Christopherson To: lirongqing Cc: pbonzini@redhat.com, vkuznets@redhat.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" On Tue, Jul 22, 2025, lirongqing wrote: > From: Li RongQing > > The commit b2798ba0b876 ("KVM: X86: Choose qspinlock when dedicated > physical CPUs are available") states that when PV_DEDICATED=1 > (vCPU has dedicated pCPU), qspinlock should be preferred regardless of > PV_UNHALT. However, the current implementation doesn't reflect this: when > PV_UNHALT=0, we still use virt_spin_lock() even with dedicated pCPUs. > > This is suboptimal because: > 1. Native qspinlocks should outperform virt_spin_lock() for dedicated > vCPUs irrespective of HALT exiting > 2. virt_spin_lock() should only be preferred when vCPUs may be preempted > (non-dedicated case) > > So reorder the PV spinlock checks to: > 1. First handle dedicated pCPU case (disable virt_spin_lock_key) > 2. Second check single CPU, and nopvspin configuration > 3. Only then check PV_UNHALT support > > This ensures we always use native qspinlock for dedicated vCPUs, delivering > pretty performance gains at high contention levels. > > Signed-off-by: Li RongQing > --- Reviewed-by: Sean Christopherson