From nobody Thu Apr 9 11:49:32 2026 Received: from mail-pg1-f201.google.com (mail-pg1-f201.google.com [209.85.215.201]) (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 839A341161B for ; Mon, 9 Mar 2026 19:31:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773084679; cv=none; b=nwUABOL34bZ6xt5FrhdYkTk26eOEjYwrxi4NGUBYF/bQSZB41dfRbyEpoxBFWXH3KeiV6ms1PPv47ysiiBRfSuXXVqnDWSBOAexpuFJLwpBKXA5KWXSNuQjV5P3oncnXtW8slF/enlKt4VUPAfzbc3cvGiDrxyeMchE4lgitFuc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773084679; c=relaxed/simple; bh=Nh7tJ/pXL5Y8LgZgxu8ghrpxcPTqp2B/CPbh/N2FO2o=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=AIxjD4xKkw9V4WsSZhEQND6c2QMfL7A7D1dL5WzXTy5IZz+YO08lAvVKlGSDxWTaTrZ55/bddUyxNr9MC6slCv5zZgBkZZPp28Owtni1jUfSuV+QvB/5vqSvrZSSAR6I6HbY6KwluN6unDIMbo4m1yuZWFBoYV15vYmIKUr6kcA= 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=T8OOh4Xp; arc=none smtp.client-ip=209.85.215.201 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="T8OOh4Xp" Received: by mail-pg1-f201.google.com with SMTP id 41be03b00d2f7-c70dd30025fso44866426a12.2 for ; Mon, 09 Mar 2026 12:31:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1773084678; x=1773689478; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:from:to:cc:subject:date:message-id:reply-to; bh=dwTNwSVWtekPolaPxHcXxrp4YHsI9DpDNNtRgjqHJNI=; b=T8OOh4XplhQwITKtupHWbpHnO9AipUvoIybVxEjI8yMS05fUcYk3dUt2Wn3nKuDYPr NwMv/6ehPFXa5pTb4Mjx8cVRpejXZElS3/blRbM21LFNEE6tJ52K0HdBfKMvgqZV3WvI byqS5d/Q4Cgx+0u/AKKUuxXc6bqikgfVOUCWC83WMRjCuU+yQ9W0XC5ji80FW0BbJcvd 9coVuRAR7u/uoBD8tpBGlxyYOq9Dwak42M2fNLZpF9wPee57q1779Q/BIVeDkQ9S9HxD ifiXyv0QFGcaKNr3PxgeLbpAbPR8VV3V2BLCG1976Pl224nL73WTtTl9sV/6Iquj129x 8nng== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1773084678; x=1773689478; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=dwTNwSVWtekPolaPxHcXxrp4YHsI9DpDNNtRgjqHJNI=; b=r/A6ECEs8ng0+6m0axwPT0X9G0fYHC34We6a+NYQXkO4Q9DlOptw0X1646xULEBnoI 6FzPw1qC66M8ZoKiz9b1mmQoaiCoamy3e299c2CXFTU9h2hgyhY6RhVppQDoqbsbfeUh FkBunSXC245yigPPP6WHXbnHCSVwAR+p2EqYlYfxJkDZfRn+IVBVVV76/FlbAlHq+PlV b2aF+YSmNjzoxcxCedmsHenIhIIfvPkaYokGflUjf5Gx6Ivip6oWXNXQWIYUttLdW+gi J3gn3hAcRBsdSI7Sm3tPh6Vhf6qupma2UxQeMTIkc0lwPmOQxVjpIOWlqJl2zOfK9iCr T3OA== X-Forwarded-Encrypted: i=1; AJvYcCUcWHJlAJ8yYqPfCxl/MZFeGPjLZVUtokd7JQ44SLIltKUBl2K6E70QstKUq+FVXNr+kXm4xNxR2be7kdw=@vger.kernel.org X-Gm-Message-State: AOJu0YxHp+ssa5oGOQkPP42yiGWiLjonjcXPjaqY3cyU3o+Lan0LBXjq Wg4KKp2sLp2/gmIOEOymOm5iG+Keh/3Erl3pD9XuYw3oD7Nd6i+D8kpPg/ylL9h43kKmCRP+XAb HIT1ecQ== X-Received: from pgbfq28.prod.google.com ([2002:a05:6a02:299c:b0:c6e:1ddf:c9ec]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:549f:b0:398:78cb:d85 with SMTP id adf61e73a8af0-39878cb252emr6354695637.13.1773084677666; Mon, 09 Mar 2026 12:31:17 -0700 (PDT) Reply-To: Sean Christopherson Date: Mon, 9 Mar 2026 12:30:59 -0700 In-Reply-To: <20260309193059.2244645-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260309193059.2244645-1-seanjc@google.com> X-Mailer: git-send-email 2.53.0.473.g4a7958ca14-goog Message-ID: <20260309193059.2244645-4-seanjc@google.com> Subject: [RFC PATCH 3/3] KVM: Expedite SRCU callbacks when freeing objects during I/O bus registration From: Sean Christopherson To: Lai Jiangshan , "Paul E. McKenney" , Josh Triplett , Paolo Bonzini Cc: rcu@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Sean Christopherson , Nikita Kalyazin , Keir Fraser Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Use the recently introduced call_srcu_expedited() when freeing the old I/O bug during device registration to avoid triggering a non-expedited grace period. Delaying the freeing of the object by a full grace period is a complete non-issue, but the grace period also gets transferred to future synchronizations, e.g. to the synchronize_srcu_expedited() invocation in kvm_swap_active_memslots(). For micro-VM use cases, effectively transferring the non-expedited grace period to memslot updates results in a meaningful delay in overall boot time. E.g. with a CONFIG_HZ=3D100 kernel, the sync triggers a ~20ms delay, increasing boot times by 15% or more. Fixes: 7d9a0273c459 ("KVM: Avoid synchronize_srcu() in kvm_io_bus_register_= dev()") Reported-by: Nikita Kalyazin Closes: https://lore.kernel.org/all/a84ddba8-12da-489a-9dd1-ccdf7451a1ba@am= azon.com Cc: Keir Fraser Signed-off-by: Sean Christopherson --- virt/kvm/kvm_main.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 9faf70ccae7a..ceaf08a03428 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -6021,7 +6021,7 @@ int kvm_io_bus_register_dev(struct kvm *kvm, enum kvm= _bus bus_idx, gpa_t addr, memcpy(new_bus->range + i + 1, bus->range + i, (bus->dev_count - i) * sizeof(struct kvm_io_range)); rcu_assign_pointer(kvm->buses[bus_idx], new_bus); - call_srcu(&kvm->srcu, &bus->rcu, __free_bus); + call_srcu_expedited(&kvm->srcu, &bus->rcu, __free_bus); =20 return 0; } --=20 2.53.0.473.g4a7958ca14-goog