From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f73.google.com (mail-pj1-f73.google.com [209.85.216.73]) (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 8EA9A18FC91 for ; Fri, 15 Aug 2025 19:28:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.73 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755286087; cv=none; b=Oe8DA2afcx3SSZsoynxwQDdB53qBV8m0b2nvL9RGO3mV8v6mpt/+A6Ojw+47GP+EJGqHIGfJ/v5IksdHd4bKXQr9h2eEUlfjoeQokYaB03rhGCKhCFxWQasY9cYc7/5Kcjs7jRS2bthYBbJfQwlMbS8XxzDPMAGaBICN4O+lmjw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755286087; c=relaxed/simple; bh=03ai3+jPXw+qIgPjJjhYeat8FHaMCcAxTtMV6J8Fauw=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=JD/joya9IuwsvjbyXYGRGqhcVDbl/worMbqh0j+kX45gxtD2B3/AT6DPTZhKsYhWZP68C4K3+Qg7pT4yY66+B4hkZOnigiytzlopGzVlF0n1guAH0bpEShqFO3SGfTdiPEfLuxsUyBz/Q2mCGOdUSBU9yTAqBDVWCEYib66eKTk= 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=209.85.216.73 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-f73.google.com with SMTP id 98e67ed59e1d1-32326779c67so2159011a91.1 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=puNp/g7xU6xiIuXdnCJMqLe7K2z0z8CUudhSo7rfJc5sMTAe+k2SzPtB6mbCNu165r mm9jYoTZN6wSMZPswiywWCdu8cr6mxI3w45yAYVfT5bMF138CCLaO55jY1i7ipgOY104 toM9EcZYWK6h9+jJJILBn2bc0wa31R/OokUwJe3c/WzRxwxauIrlWIu3ux4KcP5/B+qk 5xBVoo3dWBqMNlWGp8gUCTtDaFYOH4hQZnYhGoXcLEROSoG9CcEr1i8fbPws/f62A/S7 etzL0SyTr9GFmwXC2AJI6ByEQwTTneVQTwgm6efvDYZomq1KyELVSfqKAnK34uIgQCGt kYGw== X-Forwarded-Encrypted: i=1; AJvYcCWx/P3+T1s/45c9PxfBfpLBAd5VbWfsVAa68KynSyXkxKK+DzhI79QJC0/Y/XUg2g9hpAy1SLSOlNVKUwA=@vger.kernel.org X-Gm-Message-State: AOJu0YwBHfrl1EMvgJ0gHTax7BoX2zXqM4EDU0xUHbbf7XNkcQX+9w6g ReR+6Ks1XewCmZTHNCemoK3iRoEodTmt8gMSgTN53viUZYL4K30zsBdQy9AYcRKOkt/SnYFL4SB SmMlM0g== 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: linux-kernel@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